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mkline55
2012-Oct-22, 05:56 PM
What evidence favors the expanding universe theory from a contracting atomic theory? I am not proposing this as ATM, but I do want to investigate the differences in viewpoint. I'd rather fill my knowledge gaps with useful information than random concepts. Unfortunately, there is a lot of information available of varying quality, and I could probably spend months just trying to tell generally accepted information from not so accepted info.

In case my question is not clear, to a casual observer, an expanding universe would demonstrate some of the same general evidence (Hubble's law for example) whether it was the universe that was expanding, or the observer who was contracting. But there should also be some differences, which ought to be found in the details, perhaps in quantum mechanics and perhaps elsewhere. Since the mainstream view is that the universe is expanding, I'd like to know what details lead to that conclusion.

antoniseb
2012-Oct-22, 06:22 PM
What evidence favors the expanding universe theory from a contracting atomic theory?...
Well, for one thing, there is no contracting atomic theory... but assuming that you are asking about what if all the atoms and other particles in the universe are somehow getting smaller in some special way that keeps them all locally exactly the same size (even ones experiencing time at a very different rate because they are on the surface of a neutron star)... it would have trouble keeping planetary orbits correct, it would not by itself explain the cosmological red-shifts we see, it wouldn't explain the 2.7K microwave background radiation, or the minor temperature differences we see in it. It would need a very weird size-change formula to explain the angular sizes we see distant galaxies at, or for that matter the evolution of the concentrations of elements we see in the distant universe.

Do you have *any* practical use for such a theory?

John Jaksich
2012-Oct-22, 06:24 PM
My first question is "what is a contracting atomic theory?" I thought had heard about a lot of different theories ---but what do you mean---and upon reading your subsequent paragraph, it does remind me somewhat of a book by Brian Greene: The Fabric of the Cosmos---

Please clarify?

John Jaksich
2012-Oct-22, 06:28 PM
My first question is "what is a contracting atomic theory?" I thought had heard about a lot of different theories ---but what do you mean---and upon reading your subsequent paragraph, it does remind me somewhat of a book by Brian Greene: The Fabric of the Cosmos---

Please clarify?


to mkline55
Never mind my question.

mkline55
2012-Oct-22, 06:42 PM
Well, for one thing, there is no contracting atomic theory... but assuming that you are asking about what if all the atoms and other particles in the universe are somehow getting smaller in some special way that keeps them all locally exactly the same size (even ones experiencing time at a very different rate because they are on the surface of a neutron star)... it would have trouble keeping planetary orbits correct, it would not by itself explain the cosmological red-shifts we see, it wouldn't explain the 2.7K microwave background radiation, or the minor temperature differences we see in it. It would need a very weird size-change formula to explain the angular sizes we see distant galaxies at, or for that matter the evolution of the concentrations of elements we see in the distant universe.

Thanks. Anything besides planetary orbits, cosmological red-shift and CMB? Is Oklo supportive evidence for expansion as well?

antoniseb
2012-Oct-22, 06:57 PM
Thanks. Anything besides planetary orbits, cosmological red-shift and CMB? Is Oklo supportive evidence for expansion as well?

I don't see how Oklo (natural reactor) could be a strong decider one way or the other compared to so many other issues. Really, I just rattled a few off the cuff, I'm sure more than a minutes thought would reveal more, but since it was already ruled out by the first batch, I don't want to bother going further without really good reason.

mkline55
2012-Oct-22, 07:21 PM
I don't see how Oklo (natural reactor) could be a strong decider one way or the other compared to so many other issues. Really, I just rattled a few off the cuff, I'm sure more than a minutes thought would reveal more, but since it was already ruled out by the first batch, I don't want to bother going further without really good reason.

I apologize for being such a burden. I must have misunderstood the purpose of the questions and answers forum.

antoniseb
2012-Oct-22, 07:23 PM
I apologize for being such a burden. I must have misunderstood the purpose of the questions and answers forum.
You can ask, and you are not a burden. I'm explaining why *I* in particular aren't giving more of an answer.

mkline55
2012-Oct-22, 07:55 PM
You can ask, and you are not a burden. I'm explaining why *I* in particular aren't giving more of an answer.

I do appreciate the quick response. I'll look more into understanding those areas. As for the "why", it's a matter of learning. I find it easier to understand some theories by comparing them with the known alternatives and learning what makes one better than all the others. I've already eliminated tired light and static theories, so this comparison, which I view as the flip side of the same coin, and perhaps one other theory were all that remained. There's a lot of material out there to examine, so how can I keep from wasting endless hours researching dead ends? Ask the experts where to look next. You've already given me enough for a few days study. I'll take it from there. Thanks again.

Copernicus
2012-Oct-22, 11:02 PM
Would think that the earth would start spinning faster.

cjameshuff
2012-Oct-22, 11:21 PM
I think you could create a consistent description of a universe in which yardsticks are contracting which would be equivalent in every way to one in which lengths are expanding. However, a universe that is expanding or contracting is a result predicted and explained by general relativity. There is no theoretical framework that shrinking matter fits in, and no advantage to that interpretation.

It seems similar to the suggestion that the Earth is a hollow cavity containing the universe in the center. You could make such a description work with sufficiently convoluted mathematical transformations, but it's not a reasonable approach. For example, matter would not just have to shrink, it would have to produce and interact with shorter and shorter wavelength radiation (older light appearing to be redshifted because it was emitted at a longer length scale), and otherwise change in properties over time so that this radiation with ever-decreasing wavelength and ever-increasing energy in fact appears to have the same energy and wavelength.

mkline55
2012-Oct-23, 12:02 PM
Thanks again. I didn't want this to stray into a comparison of theories, but merely want to know what factors to consider. If I come up with a theory, I'll repost in ATM. For now, though, I am only trying to understand the evidence for expansion.

John Jaksich
2012-Oct-23, 12:12 PM
Thanks again. I didn't want this to stray into a comparison of theories, but merely want to know what factors to consider. If I come up with a theory, I'll repost in ATM. For now, though, I am only trying to understand the evidence for expansion.

I just thought I would add: sometimes to understand (to understand the evidence for expansion) you might want to not go through such a tortured path (if I am not mistaken--you sought to understand in terms that are not normally given by astronomers). Just my opinion . . .

Bob Angstrom
2012-Oct-23, 08:22 PM
I don't know of any observations that could demonstrate the difference between a universe that is expanding and a universe of constant radius in which the material contents are growing smaller. Arthur Eddington was probably the first to question whether the universe is truly expanding or if we and the rest of the material world are contracting giving us the illusion of expansion. The consequences of either possibility are identical and we lack a god's eye view from beyond the universe that could give us an outside perspective. The “answer” to this question is a matter of what we choose as our arbitrary standard of length and it forces us to examine our reasons for selecting one standard of measurement over another. Our observation that the universe is expanding is only as valid as our ability to identify something that we can consider to be absolute and unchanging in size over a cosmological length of time. If we choose to use the atomic scale as a constant, we can consider some material object such as the radius of a hydrogen atom as a unit of length equal to 1. We can then measure the radius of the universe in units of H radii to find that the universe has a radius of R so the radius of a H atom is 1/R. It makes no difference to the scale of our universe if R is expanding while 1 remains the same or if our unit 1 (the radius of an H atom) is growing smaller while R remains the same. The first possibility represents a universe of expanding space and second is a universe material contraction where expansion is an illusion "inverse expansion" and we should expect to find no physical or observable differences between the two. One scale is the simple physical and mathematical inverse of the other.

The atomic abundances suggest an early universe of extreme confinement where hydrogen atoms were able to fuse to helium. This means that the universe was either once so small that hydrogen atoms were able fuse or that hydrogen atoms were once so large that they crowded together to the point of fusion in a universe of static radius. Confinement can be explained either way and the difference is an arbitrary and subjective matter of scale. Relative to us the universe is expanding but, relative to the universe, we and everything within are growing smaller. It works the same either way.

The cosmological redshifts we observe may be considered as either short wavelengths that have been “stretched” out by the expansion of space or they may be long wavelengths emitted by atoms of proportionally greater size that are just now reaching us unchanged from their original condition in a non-expanding universe. There is no real difference between the two views except in our choice of scale and there is no need to pick one view over another because the two views are equivalent. But having two views is better than one because it enables us to test the correctness of our assumptions based on one point of view against a second equally valid point of view and that gives us perspective.

Jeff Root
2012-Oct-24, 12:39 AM
My impression has long been that the expansion is a
single event, like an explosion is a single event, while
shrinking atoms would require a vast number of separate
events all perfectly co-ordinated. Lack of this perfect
co-ordination would result in the conflicts between what
happens at different scales and under different conditions
in different places that antoniseb refers to. I can
accept the idea of a single event which involves the
entire visible Universe (and beyond) much more easily
than I can accept the idea that vast numbers of different
things, widely separated from one another and having all
manner of different properties, are all behaving in exactly
the same way in unison-- all shrinking at exactly the
rate needed to make it appear that the Universe as a
whole is expanding. In an explosion, if some of the
explosive fails to detonate, or detonates less forcefully
than the rest, it does not affect the overall picture that
an explosion is occurring. Similarly, if some parts of
the Universe did not expand as rapidly as the rest, it
would not affect the overall picture that the Universe
is expanding. But if some atoms or some galaxies did
not shrink at the same rate as the rest, we would see
some oversized atoms or oversized galaxies that would
be at odds with everything we know about matter.
The shrinkage would have to be perfectly synchronized
everywhere to prevent such mismatches from appearing
all over the place.

-- Jeff, in Minneapolis

Bob Angstrom
2012-Oct-24, 02:54 AM
My impression has long been that the expansion is a single event, like an explosion is a single event, while
shrinking atoms would require a vast number of separate
events all perfectly co-ordinated.You are right that material contraction needs to be largely the same universe wide to explain how a universal contraction of matter could appear indistinguishable from a universal expansion of space so we need to look for a single universal cause that could result in the entire atomic world growing smaller in a co-ordinated fashion. An earlier poster was on the right track when he said a material contraction of the Earth should cause the planet to spin faster. The same is true on the atomic scale. A contracting atom should spin faster as it contracts and, since our observation of time is directly linked to the motion of atoms, a contraction of the atomic scale should appear as a quickening of time. Conversely, a universal quickening of time should appear simultaneously as a universal contraction of matter where light reaching us from distant sources should appear redhsifted because it is coming from older, slower moving atoms in an older universe where time progressed at a slower pace. In this view, cosmic redshifting is explained as a quickening of time in a non-expanding universe. We can explain cosmological phenomenon as either an expansion of space with time as a constant or as a quickening of time in a non-expanding space but it makes no difference which because it works the same either way.

George
2012-Oct-24, 03:51 AM
What evidence favors the expanding universe theory from a contracting atomic theory?
Perhaps the following pieces of evidence favoring the expanding universe will be helpful. It was presented (Georges Lemaitre) as a likely result from General Relativity before any real objective evidence was known. An opposing theory would have these and more to deal with.

The Expansion of the Universe:
....> Hubble Constant (redshift) More
....> Einstein's field equations (1916) predicted an expanding (or contracting) universe
....> Time Dilation of Supernova More1 also More2
....> Gamma Ray Bursts
....> The CMBR - Cosmic Microwave Background Radiation. More
........> The wavelength (microwave)
........> The Temperature (2.73K). More
........> The Blackbody Results.
........> The "smoothness" (isotropy) [Inflation required]
........> The very small "roughness" (anisotropy) in this radiation. WMAP
........> The angular size of the "hot" spots matching predictions.
........> The power spectrum
....> Distant Cloud temperatures
....> The Element Abundances from Nucleosynthesis.
....> Helium (25%)
....> Deuterium, its relative abundance.
....> The observed Differences in Galaxies between today's and earlier ones.
........> Paucity of distant Barred Spirals.
........> Less organized distant Spirals.
........> No local Quasars.
....> The Age of the Universe in relation to Stellar Compositions.
....> Olber's Paradox resolved. More
....> Entropy - "The universe is dying" (Helmholtz & 2nd Law).
....> Galactic Superstructure of Super Clusters and Galactic Strands
....> No Ancient Objects older than 15 billion years.
....> The anisotropy found in background neutrino maping, probably.
....> The Lyman Forest morphology

The above is from my attempt, as is yours, in learning the hard evidence that supports Big Bang Theory, and is found from this thread... Big Bang Bullets (http://cosmoquest.org/forum/showthread.php/8241-Big-Bang-Bullets-gt).

[This list is 9 years old. I wonder if it needs updating?]

In addition to the above, a contraction theory would still needs a starting point; what is it we are contracting from? BBT has a starting point, though not a singularity quite yet, which has more appeal, I think, than the infinity and beyond sort of view.

Bob Angstrom
2012-Oct-24, 07:31 AM
In addition to the above, a contraction theory would still needs a starting point; what is it we are contracting from? BBT has a starting point, though not a singularity quite yet, which has more appeal, I think, than the infinity and beyond sort of view.Contraction in this case means going from large size to small in the usual sense of the word. We can examine the universe from the point of view where the universe is expanding while our material world remains constant. Or, we can look at it from the point of view where the universe maintains its enormous radius as a non-expanding constant while everything within grows smaller. In either view the entire material world (atoms, trees, mountains, galaxies, etc.) is growing smaller on a cosmic time scale relative to the radius of the universe and contraction in one view is the simple inverse of expansion in the other.

The starting point for contraction is no different from Lemaitre's “single atom” theory where a single something (singularity?) begins to differentiate into forms that we can later identify as atoms, stars, and galaxies. The movie is the same in either case except for the position of the camera and the initial size of the “single atom.” In Lemaitre's movie the camera is placed at a great distance “outside” the universe where we can watch from a safe distance as a tiny universe expands and we can measure its growing dimensions. In the contraction view, the camera is placed inside Lemaitre's “single atom” where the size of the “single atom” appears infinite since we can never see all the way to its “edge.” And here we observe the same progression of events locally. We see the world around us gradually differentiate into atoms, stars and galaxies and we see the distances between objects increase as we and all other material objects around us appear to grow smaller. We have no concept of space expanding because we have never witnessed space itself expand. How can nothing expand? We interpret the increased spaciousness of our universe as a material contraction where objects grow smaller leaving space behind. Contraction is not an opposing theory. It is the same old movie visualized as what the universe looks like from the inside rather than how it might appear to an observer on the outside.

I could also ask, What is the starting point for expansion theory? What in our universe is neither expanding nor contracting so we can say, Relative to this the universe is expanding.

mkline55
2012-Oct-24, 02:51 PM
Contraction in this case means going from large size to small in the usual sense of the word. We can examine the universe from the point of view where the universe is expanding while our material world remains constant. Or, we can look at it from the point of view where the universe maintains its enormous radius as a non-expanding constant while everything within grows smaller. In either view the entire material world (atoms, trees, mountains, galaxies, etc.) is growing smaller on a cosmic time scale relative to the radius of the universe and contraction in one view is the simple inverse of expansion in the other.

The starting point for contraction is no different from Lemaitre's “single atom” theory where a single something (singularity?) begins to differentiate into forms that we can later identify as atoms, stars, and galaxies. The movie is the same in either case except for the position of the camera and the initial size of the “single atom.” In Lemaitre's movie the camera is placed at a great distance “outside” the universe where we can watch from a safe distance as a tiny universe expands and we can measure its growing dimensions. In the contraction view, the camera is placed inside Lemaitre's “single atom” where the size of the “single atom” appears infinite since we can never see all the way to its “edge.” And here we observe the same progression of events locally. We see the world around us gradually differentiate into atoms, stars and galaxies and we see the distances between objects increase as we and all other material objects around us appear to grow smaller. We have no concept of space expanding because we have never witnessed space itself expand. How can nothing expand? We interpret the increased spaciousness of our universe as a material contraction where objects grow smaller leaving space behind. Contraction is not an opposing theory. It is the same old movie visualized as what the universe looks like from the inside rather than how it might appear to an observer on the outside.

I could also ask, What is the starting point for expansion theory? What in our universe is neither expanding nor contracting so we can say, Relative to this the universe is expanding.

Much more clearly stated than I would have managed. Thanks.

The list above provides some excellent things to research. An initial scan, though, shows I need to be careful to ensure observations weren't chosen just because they appeared to provide support, and that no other possible explanation could be afforded. The Type 1A supernova observations will require some study. Some of the examples appear to be explained equally well in either model.

One note: I was not working on a steady-state model, nor a contraction model, just on the differences between contraction and expansion. I could easily be convinced of either at this point, though, as Bob indicates, it may be impossible to differentiate.

Should this thread be moved to ATM?

Cougar
2012-Oct-24, 04:16 PM
I could easily be convinced of either at this point....

Well, if you want to be at odds with the entire scientific community, you will go with contraction.

This is a non-problem. There are plenty of problems that merit attention by thoughtful beings such as yourself. This is not one of them.

mkline55
2012-Oct-24, 05:44 PM
Well, if you want to be at odds with the entire scientific community, you will go with contraction.

Joining the majority just to be in the majority doesn't by itself make it right. I choose to question reason until I can be convinced. When it comes to the alternative viewpoints, each has some problems. One asks us to believe that everything originated from a single something that itself came from nowhere, that from the perspective of any point in the universe, other things are moving away at nearly the speed of light, and the majority of all matter in the universe is invisible, while at the quantum level, nothing ever changes since it first originated. The other extreme is that something at the quantum level could change, but everything in the universe is changing at the same rate and at the same time, however, nothing needs to be moving at any considerable speed. One of these views is simpler than the other.

Shaula
2012-Oct-24, 06:14 PM
One asks us to believe that everything originated from a single something that itself came from nowhere
No it does not. Big Bang theory ONLY states that the observable universe expanded from a hot dense state a finite time ago. It is known that the models break down before then and therefore don't say anything about it.


One of these views is simpler than the other
The way you state it maybe. Now you have to do the maths. Work out what happens to things like spectral lines, fundamental constants. Look into the scale symmetries you are breaking and what that does for the duality relationships in String theory. It rapidly becomes apparent that far from being simple the contracting universe requires a lot of things to change in lockstep for no apparent reason. It is nice and simple in GR to switch between the two co-ordinate systems but it really impacts QM.

mkline55
2012-Oct-24, 06:45 PM
The way you state it maybe. Now you have to do the maths. Work out what happens to things like spectral lines, fundamental constants. Look into the scale symmetries you are breaking and what that does for the duality relationships in String theory. It rapidly becomes apparent that far from being simple the contracting universe requires a lot of things to change in lockstep for no apparent reason. It is nice and simple in GR to switch between the two co-ordinate systems but it really impacts QM.

Spectral lines are redshifted. Fundamental constants have to be dealt with individually. Ratios likely stay the same (like pi). Measured "constants" may not be constants, but would have to be verified on a case-by-case basis. That will take some time. Don't expect me to recalculate every imaginable constant determined over the past century in a simple dialog. String theory, while a very interesting set of mathematics, leaves a lot to be desired. The reading I have done contains a heavy dose of maybes, posits, likelys, instabilities and inconsistencies. Duality appears to simply be the appearance that multiple theories have related results, indicating a better overall theory might be forthcoming, but that same principle could be said of the expansion and contraction theories.

Shaula
2012-Oct-24, 07:06 PM
The point I was making about String dualities is that it requires a form of invariance governed by the dilaton field. This in turn has a scale invariance component.

My main point was that contraction is not simpler. Not by a long way. It may be equivalent but to call it simpler is misleading

Cougar
2012-Oct-24, 07:55 PM
Joining the majority just to be in the majority doesn't by itself make it right.

This is true. But I think it is significant to add that this "majority" is not simply the majority of scientific illiterate Americans, and it's not just a 51% majority; it's more like a 99.9% majority. This is the majority of people who have studied the evidence for 10-40 years. While not absolutely conclusive, I think this should give one a very, very, very good indication about what is "right" and what is not worth wasting one's time on.


I choose to question reason until I can be convinced.

Others here have said the two models are equivalent. Even if they are, about which I have my doubts, so what? Apparently this does not change any of our observations nor our predictions. It doesn't add anything.


One asks us to believe that everything originated from a single something that itself came from nowhere....

As Shaula pointed out, the big bang theory doesn't say our Universe "came from nowhere." We simply do not know that part, and it's unclear if we ever will. But we do know that within the first 3 minutes it was extremely hot and dense, but rapidly expanding and cooling. We know that free neutrons have a half-life of about 15 minutes, after which they decay into protons, electrons, and electron neutrinos. We know that roughly 25% of the baryonic mass in the Universe is represented by helium, whose nucleus contains neutrons. We know that those helium nuclei must have resulted from nuclear fusion in the the first 3 minutes and 46 seconds, after which the Universe had expanded and cooled such that nuclear fusion was no longer possible. We know this because we've done the experiment and we've done the math. (Well, not me, specifically. :o ) Our era is one of precision cosmology. You should come along, but don't get tripped up by non-problems.

cjameshuff
2012-Oct-24, 09:29 PM
I am reasonably sure a contracting-matter model can be formulated that is equivalent in every way but one. Distant light appears redshifted because your ruler has shrunk since it was emitted. Time is increasingly fast for you because light has shorter distances to travel, making distant things time dilated as well. Both interpretations start with an extremely dense state. The CMBR is the same thing it is in the mainstream interpretation, the radiation that started propagating freely when the universe's density and temperature dropped enough for it to be transparent. You need a period of dramatically faster shrinkage to match up with inflation. The same changes in density over time give the same isotope abundances.

However, the expanding universe is a prediction from a theory based on reasoning from a few simple axioms, which so far as we can tell is an accurate representation of reality. The contracting matter picture is a weird mathematical transformation of the same description that has no particular justification for existence, and is considerably more difficult to visualize and reason about.

In On the Wild Side, Martin Gardner covered a coordinate transformation that produces a cosmology where the Earth is a hollow cavern and the entire universe is contained within it. It is equivalent in every way to the more straightforward model, and no experiment can distinguish the two, as each is just a coordinate transformation of the other. However, there's an obvious reason to prefer the simpler approach, the contortions required for the hollow Earth model are decidedly unnatural. I think contracting matter is the same...with sufficient work, you can make it mathematically equivalent, but it's hardly a reasonable approach.

Bob Angstrom
2012-Oct-25, 06:06 AM
You need a period of dramatically faster shrinkage to match up with inflation.This is an excellent observation. As a general rule contraction is something that begins slowly and then grows faster with time. Some familiar examples are a deflating balloon, a rock slide on a hill, or the World Trade Center collapse. Faster shrinkage as a match for Guth's inflation is the opposite of what we should expect in contraction theory.
The contracting matter picture is a weird mathematical transformation of the same description that has no particular justification for existence, and is considerably more difficult to visualize and reason about.
The contracting matter picture is the simple inverse of expansion which is not too weird a mathematical concept. The visualization in contraction theory is not really difficult once you get past the strangeness. Instead of the universe growing larger, the universe remains the same size while everything within grows smaller.Trying to visualize a universe of contracting matter gives us some appreciation for difficulties faced by a generation of astronomers when they had to come to grips with expansion after growing up in the tradition of a static universe. For many the transition took years if not decades. Remember Einstein's lambda? And, in the case of the steady state astronomers, they never did "grock" the concept. Now it seems strange to us that inflation theory was not immediately obvious. Personally, I find that the universe occasionally makes more sense from the contracting point of view and, once understood, the equivalent problem makes more sense in expansion theory too. The main advantage to contraction theory is that expansion and contraction are equivalent so we can compare one with another just as you did with the inflation problem. Anything that doesn't work in both sends up a flag that we have a potential problem that needs to be reconsidered. Either one conclusion or the other is wrong or we need to find a consensus that works for both. There is another mismatch between the two theories about the issue of accelerated expansion. The discovery of an accelerated expansion was a big surprise because everyone had predicted a slowing of expansion in the BBT where expansion should slow because it works against gravity. As I said earlier, acceleration is the usual condition for contraction so we should expect to see an apparent acceleration in the universal expansion as contraction accelerates. In contraction theory, cosmic expansion is an illusion and it requires no energy to accelerate an illusion. There is no need for dark energy.
Guth's inflation fails in contraction theory and accelerated expansion driven by dark energy fails in expansion theory and comparing the two theories together signals these as problem areas. The next step is to look for a consensus that works for both.*Two equivalent theories are better than one because they allow us to examine the same problem from more than a single point of view.

Shaula
2012-Oct-25, 02:06 PM
As a general rule contraction is something that begins slowly and then grows faster with time.
Only if driven. In your examples, by surface tension and by gravity. Which means that:

There is no need for dark energy.
Is not strictly true. There is still a need for a driver of this contraction. It cannot just be gravity because that would leave a signature.

mkline55
2012-Oct-25, 03:52 PM
There is still a need for a driver of this contraction. It cannot just be gravity because that would leave a signature.

What if gravity - or gravitational fields - were the signature?

Shaula
2012-Oct-25, 04:42 PM
What if gravity - or gravitational fields - were the signature?
Then you need to rebuild GR from the ground up. And it still does not answer the question about Dark Energy.

Bob Angstrom
2012-Oct-25, 04:45 PM
Only if driven. In your examples, by surface tension and by gravity. Which means that:

Is not strictly true. There is still a need for a driver of this contraction. It cannot just be gravity because that would leave a signature.The driving force behind contraction theory is an acceleration in time but it may be misleading to think of time as a driving force because material contraction and a quickening of time are simultaneous. Contraction theory doesn't stand alone but it is a part of a continuum of models that we can use to understand the cosmos and the difference in each model begins with a choice of absolutes. With contraction theory, the size of the universe is immense and unchanging so space serves as an absolute while time is an accelerating variable. In this model space appears to be expanding because we and the entire material world around us are contracting but the expansion of space is an illusion.

Expansion theory lies at the other end of the spectrum where time is an absolute and space is an expanding variable. At some remote point in time, space could begin to contract and the whole universe could end in a Big Crunch. This would be equivalent to a slowing of time in contraction theory. Anyhow, the expansion space is the driving force behind expansion theory and the acceleration of time is the driving force behind contraction theory.

There is a third and popular possibility that lies midway between these two extremes where c is an absolute and space and time are variables. In this model, space is currently expanding while time is accelerating. Time must accelerate as space expands otherwise c could not remain a constant since c=s/t. This is a combination of the two previous models where space is expanding on one hand and matter is growing smaller on the other. As particles contract, their spin and motions increase so the contraction of matter appears to us as a quickening of time. The driving force behind this model is a combination of variations of space and time that we call gravity.

The BBT fits the third model but I don't think the issue of accelerating time/contracting matter that goes along expanding space has been properly addressed.

Shaula
2012-Oct-25, 05:21 PM
The driving force behind contraction theory is an acceleration in time but it may be misleading to think of time as a driving force because material contraction and a quickening of time are simultaneous.
So to make my point again: you said the theory does not require Dark energy, which is true. What you left out was that it required some other mysterious driving factor to make things contract at a time varying rate. Contraction theory is not a simpler form of expansion theory, it is exactly analogous and has all the same complexities in it because it is just a co-ordinate transform. Any theory which has tried to be more than that has failed an observational test.

Bob Angstrom
2012-Oct-25, 08:25 PM
So to make my point again: you said the theory does not require Dark energy, which is true. What you left out was that it required some other mysterious driving factor to make things contract at a time varying rate. Whatever “mysterious driving factor” is making the universe appear larger is also making the contents of that same universe appear smaller- relatively speaking. Your question appears to be about the “First Cause” or is it more down to Earth than that?
The consensus is that the universe appears to be expanding. The question is why does the universe appear to expand? Is the universe really expanding or does the universe remain its same enormous size while we and everything within grows smaller creating the illusion of expansion? The commonality to both of these views is the observation that the universe appears to be expanding and, relative to the radius of the universe, the material within appears to be contracting. There is no physical difference between the two views and the “mysterious driving factor” is identical for both.
Contraction theory is not a simpler form of expansion theory, it is exactly analogous and has all the same complexities in it because it is just a co-ordinate transform. Any theory which has tried to be more than that has failed an observational test.I agree that contraction theory is no more than a co-ordinate transform but “simpler” is a matter of familiarity. Expansion theory is intuitively simple. We have all seen fireworks displays and explosions so it is natural to equate expansion theory with an explosion and the name encourages us to do so. The theory becomes thorny when someone questions what the universe is expanding into or how space itself can expand from within and it continues to be difficult as one has to shed their previous misconceptions about the big bang as being some kind of really big explosion in 3-D space.
I fell into contraction theory after unsuccessful attempts to visualize how the entire universe could have once been no larger than a golf ball and then I found a “simpler” way. Both theories have their thorny spots but they don't often fall in the same place.

Everything we know about the condition of space is derived from our observations of matter. This is why Mach called absolute space a “metaphysical.” It is something we can speculate about but not observe directly. In the same sense, for one to say that space is expanding is a metaphysical explanation. If we can describe cosmological change in terms of the changes we directly observe in the matter - forgetting about space- then we have an explanation that is one step less abstract and I see that as a positive.

Shaula
2012-Oct-25, 10:16 PM
Whatever “mysterious driving factor” is making the universe appear larger is also making the contents of that same universe appear smaller- relatively speaking. Your question appears to be about the “First Cause” or is it more down to Earth than that?
I don't have a question. I was simply pointing out that when you said:

As a general rule contraction is something that begins slowly and then grows faster with time.
followed up by

There is no need for dark energy.
It could have been taken as implying the contraction is somehow simpler or needs less pieces than the expansion form. My point was that you still need something. You may decide not to call it Dark Energy but a change in the rate of contraction in the universe requires a driver.

Jim
2012-Oct-26, 01:50 AM
I apologize for being such a burden. I must have misunderstood the purpose of the questions and answers forum.

Q&A is intended for providing mainstream answers to astronomy-based questions.

This thread seems to be more of a discussion than a Q&A. And some folks are actually bringing up some ATM topics.

I'll move the thread to S&T, which is intended to support discussions of scientific subjects. But let's steer clear of ATM answers.

Bob Angstrom
2012-Oct-26, 06:38 AM
It could have been taken as implying the contraction is somehow simpler or needs less pieces than the expansion form. My point was that you still need something. You may decide not to call it Dark Energy but a change in the rate of contraction in the universe requires a driver.Contraction works with gravity so I see no need for an agent to increase the rate of contraction other than gravity. Contraction should require no more pieces than expansion which implies that either contraction is lacking an exotic explanation "dark energy" or expansion has an unnecessary exotic.

Jeff Root
2012-Oct-26, 07:33 AM
Contraction works with gravity so I see no need for an
agent to increase the rate of contraction other than gravity.
The fact that the contraction works in the same direction as
gravity appears to be irrelevant. The contraction is not an
effect of gravity. It would have to have some other cause.

-- Jeff, in Minneapolis

Shaula
2012-Oct-26, 05:08 PM
What Jeff said. Otherwise we would see expansion rate vary hugely depending on local densities. We do not.

As I have said - if the contraction theory is a simple co-ordinate transform then you do need this extra term otherwise it is not going to be consistent with the expansion version. Look at the trouble things like MOND have when you start adding new terms to gravity.

cjameshuff
2012-Oct-26, 06:17 PM
As I have said - if the contraction theory is a simple co-ordinate transform then you do need this extra term otherwise it is not going to be consistent with the expansion version. Look at the trouble things like MOND have when you start adding new terms to gravity.

And any solid explanation of such effects in "contraction theory" is a similar coordinate transform away from being applied to "expansion theory", which maps much more directly onto our observations.

You might avoid the question of expanding space or contracting matter entirely, and just speak in terms of ratios of distances and size, but it looks observationally like expanding space, and there's nothing to gain in explanatory power by taking such an approach. The idea that "contraction generally increases" is certainly faulty reasoning...it's generally not true (thermal contraction, probably the most common example, slows to a stop as the object comes to thermal equilibrium), and you have no reason for associating contraction of matter to those systems where it is true.

mkline55
2012-Oct-26, 07:55 PM
What started the expansion theory? Was it an attempt to explain Hubble's observations? Was the assumption that the observed redshift could only occur because of speed? Didn't anyone consider contraction as a possibility?

Shaula
2012-Oct-26, 08:06 PM
Expansion is conceptually easier and mathematically easier before you have to start factoring in things like Dark Energy (which was not really known about until the end of the last century). It requires no fine tuned adjustments of universal constants. The observed red shift was most easily understood as a recessional effect. There simple was, and to an extent is, no real reason to reformulate this as a contraction.

Jeff Root
2012-Oct-26, 08:55 PM
The expansion theory was first put forward before there were
any observations of cosmic redshifts. That is because a static
universe would not be stable, and general relativity, which had
just been introduced by Einstein, made the necessity of either
expansion or contraction even more obvious than Newtonian
gravity had.

The theory is called the Friedmann–Lemaître–Robertson–Walker
(FLRW) metric. It is an exact solution of Einstein's field equations
of general relativity; it describes a homogeneous, isotropic
expanding or contracting universe. It was developed by Alexander
Friedmann, Georges Lemaître, Howard Percy Robertson, and Arthur
Geoffrey Walker in the 1920's and 1930's.

The discovery at about the same time that redshifts of the light
from nebulae seemed to increase with distance convinced most
astronomers that the Universe is in fact expanding. Hubble's
observation of individual stars in nearby galaxies other than
our own made it clear that those galaxies are indeed at great
distances, and pinned down the redshift-distance relationship,
although he got the value seriously wrong at first because he
misidentified some of the objects he saw in other galaxies
as Cepheid variable stars.

-- Jeff, in Minneapolis

Cougar
2012-Oct-26, 10:39 PM
The theory is called the Friedmann–Lemaître–Robertson–Walker
(FLRW) metric. It is an exact solution of Einstein's field equations
of general relativity; it describes a homogeneous, isotropic
expanding or contracting universe.

Just to clarify, here "contraction" describes the possibility that there might be enough mass in the Universe that the distance between very distant objects is getting smaller - NOT that our rulers are also contracting. Similarly, expansion means the distance between very distant objects is increasing, not that our rulers are getting longer. Like Jeff says, these mathematicians came up with these solutions before Hubble noticed the redshift-distance relation.

Cougar
2012-Oct-26, 10:51 PM
Was the assumption that the observed redshift could only occur because of speed? Didn't anyone consider contraction as a possibility?

I think this was demonstrated by direct experiment on Earth. The light from a source that was moving away from an observer was redshifted. In fact,


"Aristarkh Belopolsky verified optical redshift in the laboratory using a system of rotating mirrors."

Here is his paper from year 1900 (http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1901ApJ....13...15B&link_type=ARTICLE&db_key=AST&high=) (pdf).

Bob Angstrom
2012-Oct-26, 11:33 PM
The fact that the contraction works in the same direction as
gravity appears to be irrelevant. The contraction is not an
effect of gravity. It would have to have some other cause.

-- Jeff, in MinneapolisYes, contraction must have a cause other than gravity but gravity is important because gravity works with contraction so we can expect contraction to accelerate with time just as we should expect expansion to slow with time because expansion works against gravity.
The cause for the initial rate of contraction (or expansion in expansion theory) is part of a package deal along with things like the mass of the universe and the laws of physics. These are all part of what is called “the initial conditions” so to ask for the cause for the rate of contraction is no different from asking for the cause for the rate of the expansion of space. It just is.

Bob Angstrom
2012-Oct-27, 12:10 AM
What Jeff said. Otherwise we would see expansion rate vary hugely depending on local densities. We do not.But we do see an expansion rate of space that varies hugely with density. If space were to expand uniformly, then atoms would expand and galaxies would expand because these things are almost entirely “empty” space. If everything were to expand uniformly we would have no observation of expansion. The conventional wisdom about the BBT is that expansion applies largely to the space between galaxies but not to the space within galaxies because gravitationally bound systems do not expand. This raises the question of how matter could be so evenly distributed by expansion because expansion had to break up the primal universe which must have been the mother of all gravitationally bound systems.
In the contraction view, matter was distributed uniformly from the start and then fissures began to form as matter contracted uniformly everywhere much like the cracks in an ancient painting. I am not saying the BB explanation is either wrong or implausible. My objection is that it gives us the false impression that there is something special about the space within the galaxies that makes it immune to change and that we can draw a line between expanding and non-expanding space. In contraction theory there is no "special” space or material objects that are not in step with the universal rate of contraction. Although, locally rates may vary due to local conditions.
As I have said - if the contraction theory is a simple co-ordinate transform then you do need this extra term otherwise it is not going to be consistent with the expansion version. Look at the trouble things like MOND have when you start adding new terms to gravity.The observation of an accelerated expansion is consistent with contraction theory so there is no need to fix it. Another possibility is to review our interpretation of expansion theory to see if the exotic term "dark energy" can be removed.

Bob Angstrom
2012-Oct-27, 12:19 AM
deleted duplicate post

Bob Angstrom
2012-Oct-27, 12:30 AM
And any solid explanation of such effects in "contraction theory" is a similar coordinate transform away from being applied to "expansion theory", which maps much more directly onto our observations.

You might avoid the question of expanding space or contracting matter entirely, and just speak in terms of ratios of distances and size, but it looks observationally like expanding space, and there's nothing to gain in explanatory power by taking such an approach. The idea that "contraction generally increases" is certainly faulty reasoning...it's generally not true (thermal contraction, probably the most common example, slows to a stop as the object comes to thermal equilibrium), and you have no reason for associating contraction of matter to those systems where it is true.I agree, don't mess with gravity which is why I am dubious about dark energy. Thermal contraction is a net non-contraction globally. Heat lost from an object in one location results in thermal expansion somewhere else. It is a local observation and not part of the cosmological initial conditions of something like the rate of entropy which we should expect to remain largely the same everywhere. So the analogy doesn't apply.

Van Rijn
2012-Oct-27, 01:26 AM
I am not saying the BB explanation is either wrong or implausible. My objection is that it gives us the false impression that there is something special about the space within the galaxies that makes it immune to change and that we can draw a line between expanding and non-expanding space.


I think the false impression is yours. There is no requirement for immunity, nor are there any assumed lines. Expansion and (to even a greater degree) accelerating expansion are features that are simply too small to see in small scale features of the universe. You must instead look at very large features of the universe. Local effects of a "dark energy" (since I assume that's what you're talking about) would easily be countered by gravity. The Earth might well be very slightly larger than it would be without dark energy, but in practice the effect would be too small to detect. Imagine the force of a mosquito to lift Mt. Everest - it would make the mountain very slightly lighter, so there would be some small difference with mosquito lift versus without it, but good luck detecting it.

Bob Angstrom
2012-Oct-27, 04:34 AM
What started the expansion theory? Was it an attempt to explain Hubble's observations? Was the assumption that the observed redshift could only occur because of speed? Didn't anyone consider contraction as a possibility?Expansion theory began as a logical extension of Newton's theory of gravity which predicts an unstable universe. Edgar Allen Poe wrote about it in the 1850's.
http://en.wikipedia.org/wiki/History_of_the_Big_Bang_theory
According to Poe, the initial state of matter was a single "Primordial Particle". "Divine Volition", manifesting itself as a repulsive force, fragmented the Primordial Particle into atoms. Atoms spread evenly throughout space, until the repulsive force stops, and attraction appears as a reaction: then matter begins to clump together forming stars and star systems, while the material universe is drawn back together by gravity, finally collapsing and ending eventually returning to the Primordial Particle stage in order to begin the process of repulsion and attraction once again. This part of Eureka describes a Newtonian evolving universe which shares a number of properties with relativistic models, and for this reason Poe anticipates some themes of modern cosmology.

Arthur Eddington was probably the first to suggest contraction as a possible explanation for redshifting but he later dropped the idea in favor of expansion for reasons I don't think he ever explained. Eddington called his idea the “Shrinking Atom” theory. Russell Rierson is another person who wrote about contraction theory and he coined the term “inverse expansion." The bazaar thing about contraction is that it has occurred to who knows how many people independently as a matter of idle speculation but it is nearly impossible to explain to someone who has never independently had the same thought themselves.

Bob Angstrom
2012-Oct-27, 04:42 AM
I think the false impression is yours. There is no requirement for immunity, nor are there any assumed lines. Expansion and (to even a greater degree) accelerating expansion are features that are simply too small to see in small scale features of the universe. You must instead look at very large features of the universe. Local effects of a "dark energy" (since I assume that's what you're talking about) would easily be countered by gravity. The Earth might well be very slightly larger than it would be without dark energy, but in practice the effect would be too small to detect. Imagine the force of a mosquito to lift Mt. Everest - it would make the mountain very slightly lighter, so there would be some small difference with mosquito lift versus without it, but good luck detecting it.
I agree that there is no immunity and no lines between space that expands and space that does not. I also agree that we can't possibly observe cosmological change at the micro level. My complaint is that the way these things are usually explained gives me (and I suspect others too) the false impression that these things exist. So, if you will, explain how the space inside atoms and galaxies is expanding at essentially the same rate as space outside these elements without suggesting that somewhere we need to make a distinction between the rate of expansion for space on the inside and the space between galaxies.

Shaula
2012-Oct-27, 07:34 AM
So, if you will, explain how the space inside atoms and galaxies is expanding at essentially the same rate as space outside these elements without suggesting that somewhere we need to make a distinction between the rate of expansion for space on the inside and the space between galaxies.
Well it is pretty simple. Space is expanding at a tiny rate. Over small scales, and where there are a lot of other forces (EM, gravity) we cannot measure it because the effect is so small. but when we look over huge distances where there is little going on in (empty space) it becomes observable.

Rather like the gravity of a single proton is impossible to measure and basically has no effect on anything. But 10^40 of them is a totally different regime and gravity is pretty obvious.

Strange
2012-Oct-27, 10:57 AM
The bazaar thing about contraction is that it has occurred to who knows how many people independently as a matter of idle speculation but it is nearly impossible to explain to someone who has never independently had the same thought themselves.

I suspect that is because if someone works it out themselves, it will naturally seem "intuitive" to them. But if someone else explains it to you, you will just see it as an equivalent reformulation that is not obviously any simpler.

Regarding the expansion of space within galaxies, my understanding (quite possibly wrong) was that the evolution of the scale factor (expansion or contraction) predicted by the FLRW metric only applies to a homogeneous distribution of mass and this is only (approximately) true on cosmological scales. So we would not, necessarily, expect the same expansion where there are concentrations of mass.

Cougar
2012-Oct-27, 03:42 PM
It seems pretty easy to imagine expansion continuing indefinitely. For everything to be continually getting smaller and smaller, indefinitely, would seem to asymptotically approach the point of ridiculousness. Wasn't Martin Gardner's column titled Mathematical Games? Fine, Bob. Have fun.

caveman1917
2012-Oct-27, 05:35 PM
This relates to the way we define "distance" in cosmology. We usually take what is known as proper distance and define that as the result of laying small rods end to end between two points. On a sufficiently small scale we can unambiguously define that small rod (it is the same as what you get in SR, remember that on sufficiently small scale any GR manifold approximates minkowski). What happens then in the FLRW metric is that we see that that proper distance between points gets larger over time, which translates to saying that we can fit more small rods between them today than we could yesterday. So at the very heart of it the phenomenon is relational, it expresses something about cosmological distance compared to the small SR rods.

This can be said to be that cosmological distance grows over time, as is usually done, or it could be said that the local rods get smaller as Bob does. Both are fine really, they're both ways of framing the essentially relational statement that we get from our theory. In a sense it's a bit akin to that I can say that my car is moving or that the earth is moving as two ways to express an essentially relational statement about what my car does compared to the earth.

If Bob is more comfortable with the alternative way of putting it, then sure why not...

cjameshuff
2012-Oct-27, 05:54 PM
This can be said to be that cosmological distance grows over time, as is usually done, or it could be said that the local rods get smaller as Bob does. Both are fine really, they're both ways of framing the essentially relational statement that we get from our theory. In a sense it's a bit akin to that I can say that my car is moving or that the earth is moving as two ways to express an essentially relational statement about what my car does compared to the earth.

Or as I put it earlier, you can view it as a changing ratio of lengths to distances.

And for what it's worth, I also independently came up with the "contracting matter" view, but have never seen it as anything but a mathematical game. It's definitely not as directly related to observations, and requires rather weird phenomena such as what we see as a given wavelength of light actually shifting to shorter and shorter wavelengths over time, physical laws adjusting to keep the effects of the increased photon energy the same, making the longer wavelength photons previously emitted appear to be lower energy.

I think the comparison to the hollow universe is accurate. It may be mathematically equivalent, but it unnecessarily adds complexity and makes the relationship between theory and observations less direct.

caveman1917
2012-Oct-27, 06:56 PM
And for what it's worth, I also independently came up with the "contracting matter" view, but have never seen it as anything but a mathematical game. It's definitely not as directly related to observations, and requires rather weird phenomena such as what we see as a given wavelength of light actually shifting to shorter and shorter wavelengths over time, physical laws adjusting to keep the effects of the increased photon energy the same, making the longer wavelength photons previously emitted appear to be lower energy.

It's not as directly related to how we usually frame our observations, but then that is the point under consideration. So i wouldn't say that is much of an argument against it rather than an argument saying that if you change one perspective you have to change the rest too. It still works out after all.

Bob Angstrom
2012-Oct-28, 09:25 AM
Well it is pretty simple. Space is expanding at a tiny rate. Over small scales, and where there are a lot of other forces (EM, gravity) we cannot measure it because the effect is so small. but when we look over huge distances where there is little going on in (empty space) it becomes observable.This is a not so simple issue that troubled Mach and he illustrated the problem with the example of things like a gyroscope or the Foucault pendulum. A spinning gyroscope aligns itself with the distant stars and rotates relative to the Earth's surface in sidereal time. There must be some local effect on the orientation of a gyroscope due to the effect of gravity from the Earth and solar system but, if there is any effect, it is so small as to be undetectable. Mach explained that gravity from the Earth and sun combined is insignificant against the background of gravity from the distant stars. We now know that the distant stars amount to some two hundred billion galaxies and their combined effect is the predominant force (EM, gravity) anywhere in the universe but it is equal in all directions so we don't notice it locally. We can't divide space into places where there is a lot of gravity and (empty space) where there is “little going on” because there is little difference in the gravitational background between the two.

Shaula
2012-Oct-28, 09:41 AM
This is a not so simple issue
You asked for simple, not totally accurate. The two are generally mutually incompatible. Replace the word gravity with gravitational potential difference and you have a better explanation. The combined gravity of the rest of the universe is akin to a constant background value, forces work off differences. So the potential difference in moving one metre away from the surface of the Earth due tot he Earth is noticeable, that of moving one more metre away from some thing 10^10m away is not.


We can't divide space into places where there is a lot of gravity and (empty space) where there is “little going on” because there is little difference in the gravitational background between the two.
We can because there is a difference in the gradient. Think of it like an electric charge. If I am at +1000V and you are at 0V then you don't want to get too close. Same is true, and the effects are approximately the same, if I am at 1,000,001,000V and you are at 1,000,000,000V

Bob Angstrom
2012-Oct-29, 05:10 AM
We can because there is a difference in the gradient. Think of it like an electric charge. If I am at +1000V and you are at 0V then you don't want to get too close. Same is true, and the effects are approximately the same, if I am at 1,000,001,000V and you are at 1,000,000,000VA gravitational potential difference is what I have in mind. The gravitational background can vary from that of deep space at one end of the scale to something like the gravitational potential at the surface of a neutron star or black hole at the other. The potential difference between deep space and the space within a galaxy is not that great when compared to the entirety of the gravitational scale. Much like your example with voltage potential. So, if the expansion of space is increasing the distance between galaxies, it should also be increasing the distance between stars within the galaxies making the galaxies expand but at a lesser pace. It should also be expanding the space within atoms making them larger and there would no objects that we could say are not expanding. If the difference between space inside galaxies and space between galaxies is nothing but a gradient, then there is nothing to prevent matter of all sizes from expanding along with the expansion of space albeit at a slower pace. A small gravitational difference between the space inside a galaxy the space beyond would become apparent over a great period of time but it would diminish our ability to observe the rate of expansion if everything is expanding along with us.

Contrast this view with that of contraction theory where all material objects are growing smaller at largely the same pace leaving space behind. There are no gradients to contend with and there is no need to consider the space within galaxies to be any different from space between galaxies. It would appear from our shrinking point of view that space was expanding while the galaxies remain the same. That is the same image as the BBT but the explanations make it sound as though we have two kinds of space...gravitationally bound and unbound with a large gradient between them.

madus
2012-Oct-29, 07:15 AM
I don't know of any observations that could demonstrate the difference between a universe that is expanding and a universe of constant radius in which the material contents are growing smaller.

From Wikipedia it seems no one actually measured any distances between galaxies, but only some "effects" of expansion. Is there some reason why can't we measure the distances now and one week later and see if the distance increased?

Shaula
2012-Oct-29, 07:52 AM
From Wikipedia it seems no one actually measured any distances between galaxies, but only some "effects" of expansion. Is there some reason why can't we measure the distances now and one week later and see if the distance increased?
The precision of the measurements in nowhere near good enough to do this.

Shaula
2012-Oct-29, 07:55 AM
The potential difference between deep space and the space within a galaxy is not that great when compared to the entirety of the gravitational scale. Much like your example with voltage potential.
In that case you utterly missed the point of the example. No matter what the offsets, it is the PD that determines what happens. The offsets are irrelevant.


There are no gradients to contend with and there is no need to consider the space within galaxies to be any different from space between galaxies.
No, you just have the aforementioned hideously complex lock-step changes in a huge range of physical constants rather than just one. You take your choice, complexity will be there somewhere. Contraction based approaches are not simpler when you get into the detail of them.

Strange
2012-Oct-29, 08:09 AM
From Wikipedia it seems no one actually measured any distances between galaxies, but only some "effects" of expansion. Is there some reason why can't we measure the distances now and one week later and see if the distance increased?

Distances have been measured (which is how Hubble was able to come up with the distance / red-shift relationship). Changes in distance are too small to be measured directly.

Also, the results of making such measurements would be identical in the "expanding universe" or "shrinking ruler" case. (They would have to be, because they one is just a coordinate transform of the other).

Van Rijn
2012-Oct-29, 08:43 AM
If the difference between space inside galaxies and space between galaxies is nothing but a gradient, then there is nothing to prevent matter of all sizes from expanding along with the expansion of space albeit at a slower pace.


(Bolding added) Incorrect. Gravity can prevent it (and so can other forces). Imagine an anti-gravitational force countering the Earth's gravity, but at some extremely small fraction of a G. That isn't going to cause the matter of the Earth to come apart and fly off, but it could make the Earth very slightly less dense. But if you move away from the Earth you will eventually reach a point where gravity pulling matter towards Earth is less than the anti-gravitational force pulling matter away. Material at that and greater distances would be accelerated away from the Earth by the anti-gravitational effect.

So, you don't need two kinds of space or any of that stuff you're talking about. It's only your misconception that's the issue here.

madus
2012-Oct-29, 09:16 AM
Distances have been measured (which is how Hubble was able to come up with the distance / red-shift relationship). Changes in distance are too small to be measured directly.


Distance between Sun and Betelgeuse increases, and between Sun and Earth, and between Sun and Moon, and between Earth and Moon. Correct? And distance between Earth's south and north pole increases too? The speed with which these distances increase is the same for all? How do we calculate this speed, what number is it?




Also, the results of making such measurements would be identical in the "expanding universe" or "shrinking ruler" case. (They would have to be, because they one is just a coordinate transform of the other).

Does our measuring tape shrinks in shrinking universe?

Does our measuring tape expands in expanding universe?

Shaula
2012-Oct-29, 10:47 AM
How do we calculate this speed, what number is it?
We look at redshift relationships over a huge range of objects at different distances from us. See http://en.wikipedia.org/wiki/Edwin_Hubble#Redshift_increases_with_distance

Strange
2012-Oct-29, 12:14 PM
Distance between Sun and Betelgeuse increases, and between Sun and Earth, and between Sun and Moon, and between Earth and Moon. Correct? And distance between Earth's south and north pole increases too? The speed with which these distances increase is the same for all? How do we calculate this speed, what number is it?

These distances do not change because of cosmological expansion. They do change for a number of other reasons (for example the lunar laser ranging experiment measures the gradual movement of the moon away from the earth due to tidal effects). Cosmological expansion only occurs at scales beyond clusters of galaxies.

Expansion does not have a "speed". The distance between things increases by a proportion, which is why (apparent) recession velocity is proportional to distance: something twice as far away will have its affected twice as much.

Grey
2012-Oct-29, 03:35 PM
From Wikipedia it seems no one actually measured any distances between galaxies, but only some "effects" of expansion. Is there some reason why can't we measure the distances now and one week later and see if the distance increased?Shaula is correct, but let's put some numbers to it. Say we can measure the distance to some distant galaxy to within about 1% (that's better than we can actually do, but let's imagine that we improve things a bit). So we'll need to wait for that galaxy to move at least on the order of 1% further away for us to be able to realistically measure its changing distance directly, through repeated distance measurements. Based on current measurements of the Hubble parameter, that should take about 140 million years. So we can get these kind of results eventually, but you'll have to be a little patient. ;)

Bob Angstrom
2012-Oct-29, 09:55 PM
In that case you utterly missed the point of the example. No matter what the offsets, it is the PD that determines what happens. The offsets are irrelevant.


No, you just have the aforementioned hideously complex lock-step changes in a huge range of physical constants rather than just one. You take your choice, complexity will be there somewhere. Contraction based approaches are not simpler when you get into the detail of them.All the changes are inter-related so I don't I don't understand what you mean by irrelevant offsets.

Contraction and expansion approaches both have their complexities but they are usually not in the same place so there are often times when one approach is easier to follow than another. The reason why space and matter appear to be on divergent paths is easiest to to visualize within the contraction model. The expansion model is difficult to understand without creating a false dichotomy between what is happening inside and outside the galaxies.

Bob Angstrom
2012-Oct-29, 10:06 PM
(Bolding added) Incorrect. Gravity can prevent it (and so can other forces). Imagine an anti-gravitational force countering the Earth's gravity, but at some extremely small fraction of a G. That isn't going to cause the matter of the Earth to come apart and fly off, but it could make the Earth very slightly less dense. But if you move away from the Earth you will eventually reach a point where gravity pulling matter towards Earth is less than the anti-gravitational force pulling matter away. Material at that and greater distances would be accelerated away from the Earth by the anti-gravitational effect.

So, you don't need two kinds of space or any of that stuff you're talking about. It's only your misconception that's the issue here.How is anti-gravity not an ad hoc explanation lacking in experimental support? Besides that, your explanation has a bazaar implication. It means than an observer from inside our galaxy should see space expanding between the galaxies but not within the galaxies. This is the old balloon analogy where the balloon expands while the galaxies (the buttons) remain the same size and this is what we see. But an observer between the galaxies would have a different view. He would not see space expanding because he and his surroundings are expanding proportionally. Instead, he would see the galaxies and everything within them growing smaller at a cosmological pace. This would be an inconsistent view where expansion dominates inside a galaxy but contraction dominates on the outside and it does nothing to clarify the issue.

Shaula
2012-Oct-29, 10:39 PM
The expansion model is difficult to understand without creating a false dichotomy between what is happening inside and outside the galaxies.
No, it really is not. Expansion has its complexities but this is not one of them. I totally agree that each approach can be simpler in certain circumstances.


All the changes are inter-related so I don't I don't understand what you mean by irrelevant offsets.
That is about the concept of potential difference which seems to be a sticking point between us.

Van Rijn
2012-Oct-29, 11:46 PM
It means than an observer from inside our galaxy should see space expanding between the galaxies but not within the galaxies.


Not quite. Expansion has been observed between galaxy clusters (http://en.wikipedia.org/wiki/Galaxy_groups_and_clusters). (And then there is the acceleration of expansion, more recently discovered, at large scales.) The expansion of space isn't being directly detected, but rather by the effects on what is in space. A gravitationally bound galaxy cluster won't expand, as you now understand. It should be clear to you now that you don't need two kinds of space to fit the observations, as you were claiming.



But an observer between the galaxies would have a different view. He would not see space expanding because he and his surroundings are expanding proportionally. Instead, he would see the galaxies and everything within them growing smaller at a cosmological pace.


Actually, he would be seeing the same thing every other observer would. He could see what is happening in galaxy clusters and at larger scales just as we do. There would be no inconsistency.

madus
2012-Oct-30, 07:56 AM
Shaula is correct, but let's put some numbers to it. Say we can measure the distance to some distant galaxy to within about 1% (that's better than we can actually do, but let's imagine that we improve things a bit). So we'll need to wait for that galaxy to move at least on the order of 1% further away for us to be able to realistically measure its changing distance directly, through repeated distance measurements. Based on current measurements of the Hubble parameter, that should take about 140 million years. So we can get these kind of results eventually, but you'll have to be a little patient. ;)

I didn't mean between us and something else, I meant we take a photo and measure the distance between two galaxies with a ruler, or something among those lines. I read far away galaxies appear to be moving faster than light, so shouldn't that be enough? How fast are two most distant objects we can see moving apart one from another?

madus
2012-Oct-30, 08:04 AM
We look at redshift relationships over a huge range of objects at different distances from us. See http://en.wikipedia.org/wiki/Edwin_Hubble#Redshift_increases_with_distance

And everything is moving away from everything else with the same speed? I don't think that's possible in a dynamic universe. Why does it not happen inside solar system? Why the distance between Moon, Earth and Sun would not be increasing too? Where the effect stops? It works only in relation to galaxies, but not inside them? Galaxies do not grow bigger, or do they?

Shaula
2012-Oct-30, 08:09 AM
I didn't mean between us and something else, I meant we take a photo and measure the distance between two galaxies with a ruler, or something among those lines. I read far away galaxies appear to be moving faster than light, so shouldn't that be enough? How fast are two most distant objects we can see moving apart one from another?
Expansion as observed by us happens radially. So you would actually be measuring an even smaller effect. Taking about redshift 6 and a bit you get a recession velocity of 600,000 km/s at a range of something like 30 billion light years (that is the co-moving distance). So even it we treated this classically to make things simple then in a week your galaxy would recede 3.6e14m against a range of 2.9e26m, or 1.2e-13% change in distance. And you would be trying to measure that quantity multiplied by the sine of their angular separation.

Shaula
2012-Oct-30, 08:12 AM
And everything is moving away from everything else with the same speed?
No. They recede at the same rate. Which means that at a given distance things are moving away from us a fixed speed due to expansion. They have their own motion superimposed on top of that.


Why does it not happen inside solar system?
Might want to actually read the thread. It is discussed. Try this page for a summary: http://en.wikipedia.org/wiki/Metric_expansion_of_space

Bob Angstrom
2012-Oct-30, 08:44 AM
Actually, he would be seeing the same thing every other observer would. He could see what is happening in galaxy clusters and at larger scales just as we do. There would be no inconsistency.What is the view that observers inside a galaxy should have in common with a viewer on the outside?

I don't understand that a gravitationally bound galaxy cluster will not expand and the possibility seems remote if space is expanding.
I did claim there were two kinds of space but I was trying to explain an issue of expansion theory and slipped into an old habit of “big bang speak” where space is said to expand between galaxies but not within galaxies. This is a silly notion about the BBT that I picked up long ago because of the way expansion is explained makes it sound as though we have two kinds of space- expanding and non-expanding.

Shaula
2012-Oct-30, 08:52 AM
I don't understand that a gravitationally bound galaxy cluster will not expand and the possibility seems remote if space is expanding.
Key distinction - will not be observed to expand. Objects are not embedded to some fixed point in space, they are free to move according to the forces acting on them. Imagine a blob of water on a slope. Left alone it would slide down the slope. Now add a powerful wind blowing it sideways very fast. The down-slope motion is hardly noticeable.

madus
2012-Oct-30, 09:11 AM
Expansion as observed by us happens radially.

You mean radially away from us, as if we are in the centre of the universe? That's sounds familiar. And that's all we have, all the measurements are only in relation to us?




Taking about redshift 6 and a bit you get a recession velocity of 600,000 km/s at a range of something like 30 billion light years (that is the co-moving distance). So even it we treated this classically to make things simple then in a week your galaxy would recede 3.6e14m against a range of 2.9e26m, or 1.2e-13% change in distance. And you would be trying to measure that quantity multiplied by the sine of their angular separation.

I'm not sure how to put those number into perspective. Wouldn't resolution of the telescope play critical role, and how far can we see? How long would we need to wait in order to photograph two galaxies and see they moved one pixel away?

Strange
2012-Oct-30, 09:17 AM
You mean radially away from us, as if we are in the centre of the universe? That's sounds familiar. And that's all we have, all the measurements are only in relation to us?

But if you think about it, it is inevitably the same from every point.

Consider two galaxies A and B, where B is twice as far away. We see galaxy A receding with velocity v and B receding with velocity 2v. But from this we can conclude that B will see A moving away from it at v and us receding at 2v. So from their perspective it will appear that everything is moving radially away from them.

Shaula
2012-Oct-30, 09:17 AM
You mean radially away from us, as if we are in the centre of the universe? That's sounds familiar. And that's all we have, all the measurements are only in relation to us?
They would expand radially from us wherever we were. Hence isotropic expansion. And of course that is all we have, we are an Earthbound species.


I'm not sure how to put those number into perspective. Wouldn't resolution of the telescope play critical role, and how far can we see? How long would we need to wait in order to photograph two galaxies and see they moved one pixel away?
The telescope set up plays a huge role in all of those calculations. I even left out the bit about the precision with which we can measure distances. All of it adds up to: Not going to happen. You would need too long, more accuracy than we can get and better imaging systems than we have. Expansion is so small compared to cosmic distances. That was all the numbers were trying to get across. That even at maximum range (so large expansion rates) the change is tiny, one part in ten trillion. We only really see it thanks to the sensitivity of redshift to it and thanks to statistics.

madus
2012-Oct-30, 11:13 AM
But if you think about it, it is inevitably the same from every point.

Consider two galaxies A and B, where B is twice as far away. We see galaxy A receding with velocity v and B receding with velocity 2v. But from this we can conclude that B will see A moving away from it at v and us receding at 2v. So from their perspective it will appear that everything is moving radially away from them.

What if A and B are at the same distance away from us, but 180 degrees apart? They would be moving twice as fast away from each other than from the Earth. Is that what we measure?

Strange
2012-Oct-30, 11:18 AM
If A is moving at v and B is moving at -v (which is obviously what we observe) then A would see us receding at v and B receding at 2v. B*would see us receding at v and A receding at 2v. Isn't that obvious? And, by extension this applies to every pair of (suitably distant) galaxies.

madus
2012-Oct-30, 11:33 AM
They would expand radially from us wherever we were. Hence isotropic expansion. And of course that is all we have, we are an Earthbound species.


Speed with which galaxies are moving away from us is directly proportional to the distance? And all we measure is just radiation/light from all these different galaxies, to deduce both distance and speed, so how do we know what part of radiation readout is about distance and what part is about red/blue shift?




The telescope set up plays a huge role in all of those calculations. I even left out the bit about the precision with which we can measure distances. All of it adds up to: Not going to happen. You would need too long, more accuracy than we can get and better imaging systems than we have. Expansion is so small compared to cosmic distances. That was all the numbers were trying to get across. That even at maximum range (so large expansion rates) the change is tiny, one part in ten trillion. We only really see it thanks to the sensitivity of redshift to it and thanks to statistics.

Heh. I always imagined it as something more observable, "universe is falling apart!" kind of thing.

mkline55
2012-Oct-30, 12:14 PM
Two components of the expansion theory appear to be purely imaginary. First, dark energy. It is used to explain the apparent acceleration of expansion. To be real, dark energy would have to increase with distance, which is contrary to all other forces. Second is curvature. It appears to be little more than a theoretical explanation to keep from putting ourselves at the center of the universe. The contraction theory needs neither of these constructs. It explains the red shift equally well. Like other forces, it increases as distance decreases. It places no limit on the size of the universe. Nothing of stellar size needs to be moving at any incredible speed to make it happen. The contraction rate is easily calculated at about 1% over the past 140 million years, which is slow enough to make quantum observations appear to be constant.

madus
2012-Oct-30, 12:32 PM
Two components of the expansion theory appear to be purely imaginary. First, dark energy. It is used to explain the apparent acceleration of expansion. To be real, dark energy would have to increase with distance, which is contrary to all other forces. Second is curvature. It appears to be little more than a theoretical explanation to keep from putting ourselves at the center of the universe. The contraction theory needs neither of these constructs. It explains the red shift equally well. Like other forces, it increases as distance decreases. It places no limit on the size of the universe. Nothing of stellar size needs to be moving at any incredible speed to make it happen. The contraction rate is easily calculated at about 1% over the past 140 million years, which is slow enough to make quantum observations appear to be constant.

I think I saw someone explain gravity with that concept, would that be standard part of "contraction theory"? -- So in this theory, distance between Sun and Earth stays the same, or increases? And distance between Earth's south and north pole decreases, or stays the same? Do you have some good link about it?

caveman1917
2012-Oct-30, 01:11 PM
To be real, dark energy would have to increase with distance, which is contrary to all other forces.

First of all dark energy is not a "force" per se, secondly there are forces that increase with distance such as a spring force or the colour force.

Shaula
2012-Oct-30, 01:32 PM
Two components of the expansion theory appear to be purely imaginary. First, dark energy. It is used to explain the apparent acceleration of expansion. To be real, dark energy would have to increase with distance, which is contrary to all other forces. Second is curvature. It appears to be little more than a theoretical explanation to keep from putting ourselves at the center of the universe.
First up curvature has little to do with us being at the centre. So your second point falls over. Dark energy is a widely acknowledged placeholder until we understand what is going on a bit better. Your characterisation of DE as a force is inaccurate too - essentially that is only true for cosmological constant versions of it.


The contraction theory needs neither of these constructs. It explains the red shift equally well. Like other forces, it increases as distance decreases. It places no limit on the size of the universe. Nothing of stellar size needs to be moving at any incredible speed to make it happen.
As I have said - on the surface it looks simpler. But the minute you start doing the maths it is not. You have to posit a complex scale based set of rule for quantum effects which is not trivial no matter how simple it may seem on the outside. You have issues with the conservation of energy (just like you do in expansion theory - it becomes highly local). You also have to explain away features in the CMBR is a horribly complex way.

cjameshuff
2012-Oct-30, 02:56 PM
Speed with which galaxies are moving away from us is directly proportional to the distance? And all we measure is just radiation/light from all these different galaxies, to deduce both distance and speed, so how do we know what part of radiation readout is about distance and what part is about red/blue shift?

The red/blue shift due to random motion does not change with distance, and quickly becomes a small fraction of the overall shift. Plotting galaxies by redshift, clusters appear "smeared out" in a line pointing toward us by the motions of the component galaxies, while having a much larger overall redshift:
http://spider.ipac.caltech.edu/staff/jarrett/papers/LSS/jarrett_Fig10.jpg

So for distant objects, it's a relatively small error to begin with, and for members of clusters you can get a better estimate for distance by looking at the cluster as a whole.

Jeff Root
2012-Oct-30, 04:10 PM
It isn't apparent whether the coloration of that map follows
the actual measurements (required to make the map) or is
just illustrative.

-- Jeff, in Minneapolis

madus
2012-Oct-30, 04:10 PM
The red/blue shift due to random motion does not change with distance, and quickly becomes a small fraction of the overall shift. Plotting galaxies by redshift, clusters appear "smeared out" in a line pointing toward us by the motions of the component galaxies, while having a much larger overall redshift:
http://spider.ipac.caltech.edu/staff/jarrett/papers/LSS/jarrett_Fig10.jpg

So for distant objects, it's a relatively small error to begin with, and for members of clusters you can get a better estimate for distance by looking at the cluster as a whole.

How do we measure those distances, and can we verify with some other type of measurement?

Grey
2012-Oct-30, 04:22 PM
I didn't mean between us and something else, I meant we take a photo and measure the distance between two galaxies with a ruler, or something among those lines. I read far away galaxies appear to be moving faster than light, so shouldn't that be enough? How fast are two most distant objects we can see moving apart one from another?That won't work at all. Although the distances will change over time (although any significant motion would still be on the order of hundreds of millions of years), the angular separation won't change at all. Imagine a triangle growing larger. The sides increase in length uniformly, but the angles remain fixed. Since the angles are what matter as far as where we see something in the sky, we won't detect any change in separation over time (at least not due to cosmological expansion; the two galaxies might happen to have peculiar motion relative to each other, which we could in principle measure over millions of years, but that won't tell us anything about expansion).

HenrikOlsen
2012-Oct-30, 04:38 PM
It isn't apparent whether the coloration of that map follows
the actual measurements (required to make the map) or is
just illustrative.

-- Jeff, in Minneapolis
Since the coloration is in 7 discrete bands it's quite clear that it's for illustrative purposes, not a precise indicating of anything "real".

madus
2012-Oct-30, 04:43 PM
That won't work at all. Although the distances will change over time (although any significant motion would still be on the order of hundreds of millions of years), the angular separation won't change at all. Imagine a triangle growing larger. The sides increase in length uniformly, but the angles remain fixed. Since the angles are what matter as far as where we see something in the sky, we won't detect any change in separation over time (at least not due to cosmological expansion; the two galaxies might happen to have peculiar motion relative to each other, which we could in principle measure over millions of years, but that won't tell us anything about expansion).

You are describing it as if they are only moving away from us, but they are also moving away from each other, maybe even more so. Isn't that right? And how about if take very wide angle so we can capture two galaxies very far apart from one another, thus moving faster away from one another, I guess. Would this improve anything?

cjameshuff
2012-Oct-30, 05:05 PM
It isn't apparent whether the coloration of that map follows
the actual measurements (required to make the map) or is
just illustrative.

It is certainly not the visual color. For starters, the near end of the plot is blue and purple despite being redshifted. The maximum redshift on that plot is only at z=0.1...enough to shift blue-violet 450 nm light to blue-green 495 nm.

http://spider.ipac.caltech.edu/staff/jarrett/papers/LSS/



How do we measure those distances, and can we verify with some other type of measurement?

That plot is of simple redshift measurements. The relation of redshift to distance is calibrated using a wide variety of measurements: http://en.wikipedia.org/wiki/Cosmic_distance_ladder

cjameshuff
2012-Oct-30, 05:09 PM
You are describing it as if they are only moving away from us,

He is not. All sides of the triangle he describes grow by an identical factor...otherwise the angles would change.

Jeff Root
2012-Oct-30, 05:10 PM
You are describing it as if they are only moving away from
us, but they are also moving away from each other, maybe
even more so. Isn't that right?
Grey described the motion as everything moving apart equally.
He said:


Imagine a triangle growing larger. The sides increase in length
uniformly
A galaxy at each corner of the triangle. He specified that all
three sides increase in length uniformly. What he said was
very simple and completely clear. And basic geometry.



And how about if take very wide angle so we can capture two
galaxies very far apart from one another, thus moving faster
away from one another, I guess. Would this improve anything?
What do you think?

You are at one corner of the expanding triangle. You are
watching the other two galaxies as they move away from
you and from each other. How does the angle between the
galaxies change? Answer: It doesn't change. The angle
between the galaxies remains constant as they move apart.
Middle-school geometry.

-- Jeff, in Minneapolis

Grey
2012-Oct-30, 05:11 PM
You are describing it as if they are only moving away from us, but they are also moving away from each other, maybe even more so. Isn't that right? And how about if take very wide angle so we can capture two galaxies very far apart from one another, thus moving faster away from one another, I guess. Would this improve anything?No, that wouldn't help. You're not getting it. Think about the triangle. Draw any triangle you want, and pick one point to be us. The angle between the two sides that meet at that point will be the angular separation between the two objects. Now, let the triangle expand. Cosmological expansion is proportional to the distance involved, so each side should increase proportionally. For example, you could double the length of each side, or increase each side by 50%, or by 10%, or whatever. You'll see that the angles of the triangle haven't changed at all. So the linear distance between all galaxies increases over time, but the position in the sky doesn't change at all.

If that's still not helping you, try thinking about this situation. Imagine a ring of galaxies surrounding us, with each galaxy 10 degrees away from the next one (so a total of 36 galaxies, forming a complete 360 degrees). Now let the ring of galaxies expand uniformly. All the galaxies are getting further away from all the others, but will there ever be a point when the separation between each galaxy and the next one will be 11 degrees? Of course not, because then you'd have 396 degrees, more than a full circle, which obviously isn't possible. No matter how far away the galaxies get from you and from each other, the angular separation will remain constant. The 36 galaxies will be even spaced around a full 360 degree circle, so there will always be 10 degrees of separation between them.

Bob Angstrom
2012-Oct-30, 09:30 PM
Key distinction - will not be observed to expand. Objects are not embedded to some fixed point in space, they are free to move according to the forces acting on them. Imagine a blob of water on a slope. Left alone it would slide down the slope. Now add a powerful wind blowing it sideways very fast. The down-slope motion is hardly noticeable.I don't see any conflict in our views about “potential differences” and your observation that a galaxy “will not be observed to expand” makes sense to me be because it appears to apply to the metrics rather than placing labels on everything and saying this is “expanding” and this not. Expansion and contraction are relative and subjective terms but explanations of the BBT tend to treat them as some kind of absolutes and that is my complaint.

In your analogy with the blob of water, what are the two opposing forces related to slope and wind. I understand the water to be like a massive body such as a star far from the center of a galaxy. Gravity is drawing the star towards the center but centrifugal force acts in the opposite direction so we have a static orbit. The cosmological expansion of space should apply everywhere if we have only one kind of space, even within a galaxy, so the expansion of space should cause star's orbit to expand. But what causes the orbit to contract against the expansion of space to preserve our image of a static orbit in a non-expanding galaxy? We can't quite say that a galaxy is gravitationally bound and therefore expanding space can't cause it to expand because space is one half of what gravity is. The other half is time. The same applies to anti-gravity because anti-gravity would just be spacetime curved in the opposite direction. I think the answer must lie in the changes in time that accompany changes in space. The problem is simple in contraction theory but it becomes complex in the BBT and the only conclusion I can come up with is that the galaxy (matter) is contracting while space is expanding so we observe a galaxy that does not appear to expand. This is not the way it is normally explained.

Van Rijn
2012-Oct-30, 09:49 PM
First up curvature has little to do with us being at the centre. So your second point falls over. Dark energy is a widely acknowledged placeholder until we understand what is going on a bit better. Your characterisation of DE as a force is inaccurate too - essentially that is only true for cosmological constant versions of it.


Just to expand on this a little, what is primarily being discussed when the term "dark energy" is used, is the evidence for accelerating expansion. The term "dark energy" suggests a cause, unfortunately, but what you really should be thinking about when you hear the term is not the cause (where there are guesses, but nothing solid), but the solidly established observations that do point to accelerating expansion .


There was a somewhat similar issue with quasars: For many years, observation was ahead of theory. Astronomers were observing them, but what caused them was a mystery. There were a number of ideas about the cause, and eventually a combination of improving observational capability and more theoretical work led to the current consensus involving SMBHs.

Shaula
2012-Oct-30, 09:53 PM
We can't quite say that a galaxy is gravitationally bound and therefore expanding space can't cause it to expand because space is one half of what gravity is.
I think that this is the crux of the issue. Gravity is not a static property of spacetime - it is associated with a body and does not just passively expand with metric expansion. Gravity is not spacetime, it is a warping of it by stress-energy.

But YMMV. You seem happy to gloss over the real complexities in contracting views, but get hung up on what I see as minor complexities of expansion theory. I guess it is just how our minds see things.

Van Rijn
2012-Oct-30, 10:16 PM
Actually, he would be seeing the same thing every other observer would. He could see what is happening in galaxy clusters and at larger scales just as we do. There would be no inconsistency.What is the view that observers inside a galaxy should have in common with a viewer on the outside?


I already said it. Read the text you quoted.



I don't understand that a gravitationally bound galaxy cluster will not expand and the possibility seems remote if space is expanding.


Why? Just as with the anti-gravity analogy with Earth I gave you (http://cosmoquest.org/forum/showthread.php/138917-Supporting-evidence-for-the-expanding-universe/page2?p=2075560#post2075560), given that the magnitude of the effect of expansion is so much smaller than the strength of gravity in a cluster of galaxies, the most you should expect is that the galaxy cluster would be very slightly less dense due to the effect of expansion.


I did claim there were two kinds of space but I was trying to explain an issue of expansion theory and slipped into an old habit of “big bang speak” where space is said to expand between galaxies but not within galaxies. This is a silly notion about the BBT that I picked up long ago because of the way expansion is explained makes it sound as though we have two kinds of space- expanding and non-expanding.

Well, you either read a misleading explanation or you misunderstood it. Space can be expanding exactly the same everywhere, but that doesn't mean that the forces holding objects together will be ignored. (Unless the expansion becomes extreme - see the Big Rip hypothesis (http://en.wikipedia.org/wiki/Big_Rip).)

Jeff Root
2012-Oct-31, 01:36 AM
You seem happy to gloss over the real complexities in
contracting views, but get hung up on what I see as minor
complexities of expansion theory.
Bob,

That expresses my impression, too. I'd only modify what
Shaula said to say the complexity you seem to be hung up
on is "very minor" compared to the terrible complexity
of contracting objects. What strikes me as particularly
weird is that the complexity of contraction is exactly the
same as the complexity of expansion you complain of, except
that it would be happening at every level, not just one level.
With expansion, there is a simple difference between objects
which are bound together (by gravity or any other force) and
objects which are not bound together. That matters to the
cosmic expansion only at the level of distances between
clusters of galaxies. With contraction, you have to explain,
for example, why the orbits of the planets shrink when the
Sun and the Earth shrink. Gravity doesn't explain it, the way
it does in the case of expansion. You have that problem at
every level with the contraction idea, but only at one level
with expansion, where there is a perfectly natural, simple,
and pretty obvious explanation for it.

-- Jeff, in Minneapolis

Jeff Root
2012-Oct-31, 01:48 AM
... given that the magnitude of the effect of expansion is
so much smaller than the strength of gravity in a cluster of
galaxies, the most you should expect is that the galaxy
cluster would be very slightly less dense due to the effect
of expansion.
Bob,

It isn't clear to me that you grok this. Things which are
bound together by gravity or any other force would not be
expanding due to an all-pervading expansive mechanism.
They would simply be slightly less compacted than they
would be without the mechanism. If the mechanism of
expansion has constant, unchanging strength over time,
then the densities of bound objects would not change,
while widely-separated clusters of galaxies move apart
from one another.

-- Jeff, in Minneapolis

Jeff Root
2012-Oct-31, 02:07 AM
Thinking about what I just wrote, I wonder:

If the mechanism of expansion is all-pervading, does that
mean measurements of the strengths of the fundamental
forces are very slightly affected by it? Would gravity, seen
as always an attractive force, actually be slightly stronger
than it is measured to be? Would attractive electrostatic
forces actually be slightly stronger than measurements
show them to be? Would repulsive electrostatic forces
actually be slightly weaker than measurements show
them to be?

-- Jeff, in Minneapolis

mkline55
2012-Oct-31, 12:05 PM
You have that problem at
every level with the contraction idea, but only at one level
with expansion, where there is a perfectly natural, simple,
and pretty obvious explanation for it.

Not perfect, not natural, not simple and not obvious.

mkline55
2012-Oct-31, 12:07 PM
First of all dark energy is not a "force" per se

What would you call something that results in acceleration?

Jeff Root
2012-Oct-31, 12:10 PM
It is obvious to me, after having read about it.

What prompts you to say it isn't natural or simple?

-- Jeff, in Minneapolis

mkline55
2012-Oct-31, 12:22 PM
You seem happy to gloss over the real complexities in contracting views, but get hung up on what I see as minor complexities of expansion theory. I guess it is just how our minds see things.

In contrast, the complexities of an expansion view are enormous, while contraction requires no more than one mechanism. Expansion requires a big bang, that some view as starting at a single point (in what?) and others view as existing everywhere at once. It requires the belief that something existed to cause this to occur, and that it is even now accelerating at the cost of an impossible amount of energy coming from the "dark". It requires the near-instantaneous creation of all matter in the entire universe in just a few moments.

Cougar
2012-Oct-31, 12:53 PM
In contrast, the complexities of an expansion view are enormous, while contraction requires no more than one mechanism. Expansion requires a big bang, that some view as starting at a single point (in what?) and others view as existing everywhere at once. It requires the belief that something existed to cause this to occur, and that it is even now accelerating at the cost of an impossible amount of energy coming from the "dark". It requires the near-instantaneous creation of all matter in the entire universe in just a few moments.

Careful. If you doubt hard enough, you might just suddenly cease to exist.

Shaula
2012-Oct-31, 03:27 PM
It requires the near-instantaneous creation of all matter in the entire universe in just a few moments.
So. Where did the universe of contraction theory come from? You made you problem worse. In this formulation the entire universe came into being in one burst. All the complexity we see out there just happened. You also have to explain the Cosmic Microwave Background Radiation spectrum without a surface of last scattering.


while contraction requires no more than one mechanism
One immensely complicated mechanism. You keep saying it is simple. That is false. It is not simple because so much of physics has to change in lockstep. Your one mechanism is essentially a way to package up all the complexities of expansion into one box and say "See! One box! Simpler!" - all the complications are still there, you have just given them one name.


What would you call something that results in acceleration?
Whatever that something is. In this case a change in the metric expansion of space.

caveman1917
2012-Oct-31, 03:48 PM
What would you call something that results in acceleration?

What i mean is that dark energy as a cosmological constant is not expressed as a force per se in GR, just as the slowing down of expansion due to mutual gravity is not expressed as a force like in newtonian gravity. Which means that the argument that it cannot be real because you think it is not akin to other forces you know is flawed.

Strange
2012-Oct-31, 03:53 PM
In contrast, the complexities of an expansion view are enormous, while contraction requires no more than one mechanism.

I have to agree that this seems to be because you haven't thought through all the details.

Because these are just different views of the same thing, anything that exists in one, must exist in the other. So there must be some "equivalent" to dark energy to cause accelerating contraction.

For example, where does the CMB come from in this model? If we think of the universe as expanding, then it is natural to think it was once hot and dense, leading to a series of changes that released the radiation that became the CMB. How does that work in the contracting view?

mkline55
2012-Oct-31, 07:55 PM
I have to agree that this seems to be because you haven't thought through all the details.

I could say the same. Quantum theory assumes the existence of many absolute constants. Why? Just because it makes doing the math easier?

Strange
2012-Oct-31, 08:00 PM
OK. But how does the contracting version of the theory explain the CMB?

mkline55
2012-Oct-31, 08:47 PM
OK. But how does the contracting version of the theory explain the CMB?

As the theories regarding CMB and the observational evidence evolved over several decades, please allow me a few days to put together a response. As I understand it, CMB or something like it was theorized many years ago, because expansion required some sort of beginning, and extensive thought went into how that would have happened. The theories at the time assumed something might have been left over. When CMB was observed, expansionists quickly jumped on the idea, and claimed it as proof. Now, as can be seen from the conversational tone, expansion is seen by many as the one and only possible cause of CMB, and no one is looking at any other possibility.

Shaula
2012-Oct-31, 09:10 PM
Now, as can be seen from the conversational tone, expansion is seen by many as the one and only possible cause of CMB, and no one is looking at any other possibility.
Rubbish. Lots of people have tried to come up with plausible alternative mechanisms. They have failed.


I could say the same. Quantum theory assumes the existence of many absolute constants. Why? Just because it makes doing the math easier?
How do you think having measured constants is making the maths easier?

You seem to be skipping over my question so I will put it again: Where did the universe that is contracting come from, what was its t0 state?

Strange
2012-Oct-31, 09:12 PM
Where did the universe that is contracting come from, what was its t0 state?

And can it keep contracting forever?

Strange
2012-Oct-31, 09:14 PM
please allow me a few days to put together a response.

See, you haven't thought about the complexities! :)

Seriously, it would be interesting to see what you come up with. I have an idea, but I'm not sure it works...

Bob Angstrom
2012-Nov-01, 01:59 AM
Gravity is not a static property of spacetime - it is associated with a body and does not just passively expand with metric expansion. Gravity is not spacetime, it is a warping of it by stress-energy.Space is an integral part of spacetime and no matter how strongly it may be warped the space part can't be wrung out.
I wasn't aware that stress-energy was the force behind gravity and are you saying Newton's G is not a constant?
Resistance to the metric of expansion is usually called inertia.

Bob Angstrom
2012-Nov-01, 02:27 AM
What strikes me as particularly
weird is that the complexity of contraction is exactly the
same as the complexity of expansion you complain of, except
that it would be happening at every level, not just one level.
The complexities are usually not at the same point so there are times when one theory makes it easier than the other to understand a particular difficulty. The main advantage is that we can use one theory to test the correctness of our conclusions in the other.

That, "just one level" part makes no sense.

With expansion, there is a simple difference between objects
which are bound together (by gravity or any other force) and
objects which are not bound together. That matters to the
cosmic expansion only at the level of distances between
clusters of galaxies. With contraction, you have to explain,
for example, why the orbits of the planets shrink when the
Sun and the Earth shrink.There are no material objects that are not bound together by gravity since gravity pervades the entire universe. The distant galaxies are bound together by gravity just as the stars within galaxies are bound together only to a lesser degree.
Separating matter into bound and unbound seems little better to me than separating space into expanding and non-expanding.

Cosmic changes can only be observed across extreme distances of space and time and they are not apparent in local conditions like our solar system.

If the sun and Earth were to shrink to the size melons, would it change their orbits?

Bob Angstrom
2012-Nov-01, 02:37 AM
As the theories regarding CMB and the observational evidence evolved over several decades, please allow me a few days to put together a response. As I understand it, CMB or something like it was theorized many years ago, because expansion required some sort of beginning, and extensive thought went into how that would have happened. The theories at the time assumed something might have been left over. When CMB was observed, expansionists quickly jumped on the idea, and claimed it as proof. Now, as can be seen from the conversational tone, expansion is seen by many as the one and only possible cause of CMB, and no one is looking at any other possibility.This paper has a good historical review. The CMBR was predicted and observed in non-expansion models prior to Penzias and Wilson and it was considered to be the “temperature of space” where non-luminous matter in deep space was heated by the presence of stars (later galaxies of stars) to about 3 K. The early BBT predicted a second source of heat from the surface of last scattering in addition to heat from stellar fusion and when P-W rediscovered the 3.7K they attributed it to residual heat from the BB and heat from stellar fusion was forgotten. http://redshift.vif.com/JournalFiles/Pre2001/V02NO3PDF/V02N3ASS.PDF

Bob Angstrom
2012-Nov-01, 02:56 AM
And can it keep contracting forever?This is overly speculative but expansion and contraction have different eschatologies. Contraction theory answers the question of whether the universe is open or closed in favor of closed. The Planck distance may provide a lower limit to contraction. If particle sizes begin to slip below the Planck length, the material objects they make up may dissolve into a fog of chaos- possibly to do it all again at a later time.

cjameshuff
2012-Nov-01, 02:57 AM
Space is an integral part of spacetime and no matter how strongly it may be warped the space part can't be wrung out.
I wasn't aware that stress-energy was the force behind gravity and are you saying Newton's G is not a constant?

It's not a force, the source of spacetime curvature (http://en.wikipedia.org/wiki/Stress–energy_tensor), the result of that curvature being gravity. And no, he's not saying G isn't constant, or anything that can reasonably be mistaken for that.



Resistance to the metric of expansion is usually called inertia.

...no, it isn't.



There are no material objects that are not bound together by gravity since gravity pervades the entire universe. The distant galaxies are bound together by gravity just as the stars within galaxies are bound together only to a lesser degree.

No, they aren't. Only clusters of relatively close galaxies are gravitationally bound.



Separating matter into bound and unbound seems little better to me than separating space into expanding and non-expanding.

That's absurd. The universe is clearly not gravitationally bound overall, but there is nothing to suggest that spacetime is divided into expanding and non-expanding parts.

Shaula
2012-Nov-01, 06:54 AM
Space is an integral part of spacetime and no matter how strongly it may be warped the space part can't be wrung out.
Missing the point entirely. The point is that gravity is a dynamic effect that happens to spacetime so there is no reason things cannot move under the effects of gravity while still undergoing the effect of metric expansion.


I wasn't aware that stress-energy was the force behind gravity and are you saying Newton's G is not a constant?
It is and I was not. http://en.wikipedia.org/wiki/Energy%E2%80%93momentum_tensor talks about the stress-energy (or energy-momentum or stress-energy-momentum) tensor. It is core to GR and why saying that in GR mass warps spacetime is a gross oversimplification.


Resistance to the metric of expansion is usually called inertia.
Really isn't. No idea where you got this from.


If particle sizes begin to slip below the Planck length, the material objects they make up may dissolve into a fog of chaos- possibly to do it all again at a later time.
What theoretical underpinning supports this idea? Or does it just sound nice? What is a fog of chaos? How do fogs of chaos give birth to enormous universes ready to contract? What about entropy?


There are no material objects that are not bound together by gravity since gravity pervades the entire universe.
Yes there are. Any system is which the thermal fluctuations are sufficient to overcome the gravitational forces, any system in which electric charge or strong forces overcomes gravity is not bound. You seem to be making a ridiculous definition of gravitationally bound here to try to win a point. Just because something may feel an immeasurably small force due to gravity (which might be cancelled by the gravity from somewhere else - another unbound system) does not mean it is bound.

mkline55
2012-Nov-02, 12:57 PM
Addressing CMB as the "definitive proof" of expansion: CMB was predicted to result in an ambient temperature with no input from energy-emitting stars in the current universe. As the paper referenced by Bob Armstrong discusses, that background temperature was predicted prior to that time as being a direct result of stellar energy. So, if one were to assume CMB was the result of some big bang, then the additional stellar energy input would have raised the overall temperature. We do not see a number higher than that predicted by big bang alone, hence CMB may actually be evidence that no big bang occurred.

tusenfem
2012-Nov-02, 01:57 PM
Addressing CMB as the "definitive proof" of expansion: CMB was predicted to result in an ambient temperature with no input from energy-emitting stars in the current universe. As the paper referenced by Bob Armstrong discusses, that background temperature was predicted prior to that time as being a direct result of stellar energy. So, if one were to assume CMB was the result of some big bang, then the additional stellar energy input would have raised the overall temperature. We do not see a number higher than that predicted by big bang alone, hence CMB may actually be evidence that no big bang occurred.


Okay, mkline55, you can take this directly to ATM, if you want to defend this position.
Keep this thread mainstream please!
And Apeiron is not a mainstream journal.

mkline55
2012-Nov-02, 02:56 PM
Okay, mkline55, you can take this directly to ATM, if you want to defend this position.
Keep this thread mainstream please!
And Apeiron is not a mainstream journal.

I certainly understand and appreciate that position. I had questioned earlier whether this thread should be moved. My original question was simply asking why one position was chosen over the other. I had believed that would be easily answered. Since it has drifted somewhat, can I move the thread myself, or should I start a new one?

mkline55
2012-Nov-02, 03:18 PM
And Apeiron is not a mainstream journal.

I also meant to ask where I can find the list of mainstream journals, so I can avoid using unacceptable references in the future.

Cougar
2012-Nov-02, 04:08 PM
The CMBR was predicted and observed in non-expansion models prior to Penzias and Wilson and it was considered to be the “temperature of space”....

This is extraordinarily misleading. First of all, these early estimates of the total effect of starlight has nothing to do with a microwave background. Last time I looked, stars were not emitting all their radiation in the microwave region of the spectrum. Second of all, these early estimates considered the Milky Way galaxy to be the entire Universe. Do you think the fact that the estimators overlooked over a hundred billion other galaxies in the Universe might have led to a conclusion that was slightly off? If you or mkline are seriously questioning the current understanding of the Cosmic Microwave Background Radiation, then I would have to conclude that you are not only very, very ill-informed, but apparently purposely so.

mkline55
2012-Nov-02, 05:26 PM
This is extraordinarily misleading. First of all, these early estimates of the total effect of starlight has nothing to do with a microwave background. Last time I looked, stars were not emitting all their radiation in the microwave region of the spectrum. Second of all, these early estimates considered the Milky Way galaxy to be the entire Universe. Do you think the fact that the estimators overlooked over a hundred billion other galaxies in the Universe might have led to a conclusion that was slightly off? If you or mkline are seriously questioning the current understanding of the Cosmic Microwave Background Radiation, then I would have to conclude that you are not only very, very ill-informed, but apparently purposely so.
Your passionate defense is admirable. I don't think there's any purpose behind information, well or ill-informed, unless you suspect a conspiracy of some sort. Back (once again) to the original question, I am trying to determine why all the factors exclude any possibility other than expansion. Theories have been evolving over a number of years, so I had expected to find clear differences or at least overwhelming evidence. As yet, each apparently deciding factor has had multiple explanations or multiple viewpoints.

madus
2012-Nov-02, 05:40 PM
Grey described the motion as everything moving apart equally.
He said:

A galaxy at each corner of the triangle. He specified that all
three sides increase in length uniformly. What he said was
very simple and completely clear. And basic geometry.


Not quite. He did not say "all sides", he said:
- "The sides increase in length uniformly, but the angles remain fixed."

If all three sides were increasing in length uniformly then obviously all the angles would stay the same, and so there should be no "but". Having "but" in that sentence suggested to me he is not talking about all three sides.

Anyway, while you were explaining what's trivial you missed to realize that what I said would not actually make any difference. If even just the two sides of the triangle grow uniformly the third side will automatically follow and the angles in the triangle would again stay the same.

madus
2012-Nov-02, 05:48 PM
He is not. All sides of the triangle he describes grow by an identical factor...otherwise the angles would change.

Imagine letter V and two galaxies on each end at the top, that's what we measure, that's the only angle we can actually see. Now move each galaxy at any speed you like and this angle will stay the same. What I'm saying is that measurements relay on some mapping of light intensity, so if galaxies, for example, instead of moving away were just fading in light intensity, for some reason, we would get about the same measurement. Right? -- Tell me this, can we actually measure the distance to some galaxy today, wait a few weeks then measure the same distance and see it actually increased, or is that difference in distance out of our resolution range too?

Cougar
2012-Nov-02, 06:33 PM
I am trying to determine why all the factors exclude any possibility other than expansion.

Well, basically, it's a matter of numerous independent methods of investigation all coming together and yielding a coherent and consistent picture. There are books written about all the details, meaning it would be difficult to summarize the last several decades of development in an internet posting....

Grey
2012-Nov-02, 06:53 PM
Not quite. He did not say "all sides", he said:
- "The sides increase in length uniformly, but the angles remain fixed."

If all three sides were increasing in length uniformly then obviously all the angles would stay the same, and so there should be no "but". Having "but" in that sentence suggested to me he is not talking about all three sides.

Anyway, while you were explaining what's trivial you missed to realize that what I said would not actually make any difference. If even just the two sides of the triangle grow uniformly the third side will automatically follow and the angles in the triangle would again stay the same.I'm not sure what your complaint is here. I did mean all three sides, and since it seemed like you were still confused, I clarified that further in a later post. The "but" is pretty clearly to contrast the non-changing of the angles with the changing of the sides, rather than to suggest that I was only talking about two of the sides changing (which doesn't really make much sense: if only two sides change while the third stays fixed, the angles cannot remain the same). If you've got any other questions about what I intended to say, please feel free to ask, rather than speculating about my meaning.

But the important point, which you actually seem to be restating here, is that the angles remain fixed, so the position of two galaxies in the sky will not change, even though they are getting steadily farther apart due to cosmological expansion. I'm happy to see that you seem to agree with that now.

Grey
2012-Nov-02, 06:58 PM
Tell me this, can we actually measure the distance to some galaxy today, wait a few weeks then measure the same distance and see it actually increased, or is that difference in distance out of our resolution range too?As has been said several times now, being able to directly measure the movement of galaxies in this manner (and have a large enough change that it's outside the measurement error), the two measurements would need to be hundreds of millions of years apart. The difference between measurements a few weeks apart is much, much too small to be measured.

cjameshuff
2012-Nov-02, 07:12 PM
Not quite. He did not say "all sides", he said:
- "The sides increase in length uniformly, but the angles remain fixed."

If all three sides were increasing in length uniformly then obviously all the angles would stay the same, and so there should be no "but". Having "but" in that sentence suggested to me he is not talking about all three sides.

...

Really? You are going to ignore the rest of the sentence which explicitly states that the transformation is uniform and that the angles remain fixed, and prefer an interpretation that directly contradicts both parts of the description and the conclusion he draws based on the ambiguity of the word "but"?



Anyway, while you were explaining what's trivial you missed to realize that what I said would not actually make any difference. If even just the two sides of the triangle grow uniformly the third side will automatically follow and the angles in the triangle would again stay the same.

I'm baffled how you can come up with this response. Jeff's post explains exactly the point you accuse him of missing, except his phrasing is clearer than yours.



Imagine letter V and two galaxies on each end at the top, that's what we measure, that's the only angle we can actually see. Now move each galaxy at any speed you like and this angle will stay the same.

In uniform expansion, as Grey described (http://cosmoquest.org/forum/showthread.php/138917-Supporting-evidence-for-the-expanding-universe?p=2076070#post2076070), yes.



What I'm saying is that measurements relay on some mapping of light intensity, so if galaxies, for example, instead of moving away were just fading in light intensity, for some reason, we would get about the same measurement. Right?

A quick review of the thread verifies that no, you didn't say that. You instead suggested measuring the angular separation between galaxies.

And no, light intensity is not the only method, though it is a major one. The results are consistent with relative distance measured by redshift. Absorption of light leads to distinct effects on the spectrum of that light, and we have other checks that let us estimate the actual brightness of galaxies, such as using their rotation rate or the spread of star velocities to estimate their mass and size. There is no theoretical or observational reason to think light is somehow dimming due to some other cause, and if such an effect did exist, it would only mean our distance scale is off...it could not make a non-expanding universe appear to expand.



-- Tell me this, can we actually measure the distance to some galaxy today, wait a few weeks then measure the same distance and see it actually increased, or is that difference in distance out of our resolution range too?

You're talking about objects billions of light years away. How big a fraction of "billions of years" are you willing to wait?

madus
2012-Nov-02, 07:38 PM
...if only two sides change while the third stays fixed, the angles cannot remain the same.


The third side can not stay fixed if any of the other two sides change. And no, if the two sides change uniformly then the third side follows automatically and all the angles would stay the same.

madus
2012-Nov-02, 08:17 PM
...

Really? You are going to ignore the rest of the sentence which explicitly states that the transformation is uniform and that the angles remain fixed, and prefer an interpretation that directly contradicts both parts of the description and the conclusion he draws based on the ambiguity of the word "but"?


It does not contradict as all the angles would remain the same even if only two sides change uniformly. I was simply asking if I understood him correctly.




I'm baffled how you can come up with this response. Jeff's post explains exactly the point you accuse him of missing, except his phrasing is clearer than yours.


Do you agree that even if only two sides change uniformly all the angles would remain the same?





A quick review of the thread verifies that no, you didn't say that. You instead suggested measuring the angular separation between galaxies.


I was getting to it when I asked you about how do we know what part of reading relates to distance and what part to red shift. Before that I was asking about measuring angular separation, not suggesting anything. I know/knew almost nothing about this expansion theory, I'm just asking questions. Cheer up, already!




And no, light intensity is not the only method, though it is a major one. The results are consistent with relative distance measured by redshift. Absorption of light leads to distinct effects on the spectrum of that light, and we have other checks that let us estimate the actual brightness of galaxies, such as using their rotation rate or the spread of star velocities to estimate their mass and size. There is no theoretical or observational reason to think light is somehow dimming due to some other cause, and if such an effect did exist, it would only mean our distance scale is off...it could not make a non-expanding universe appear to expand.


What about interference, diffraction, refraction, scattering and such? What about dark mater, does it have no impact on em-waves?





You're talking about objects billions of light years away. How big a fraction of "billions of years" are you willing to wait?

What does it matter how far away they are? The further the better as that means they would be moving away faster, even faster than light, right? -- So what is our resolution, when we measure the distance to the furthest galaxies, what's the error estimate, plus-minus what?

Strange
2012-Nov-02, 08:24 PM
Do you agree that even if only two sides change uniformly all the angles would remain the same?

Basic trigonometry says no.

madus
2012-Nov-02, 08:24 PM
As has been said several times now, being able to directly measure the movement of galaxies in this manner (and have a large enough change that it's outside the measurement error), the two measurements would need to be hundreds of millions of years apart. The difference between measurements a few weeks apart is much, much too small to be measured.

Before we were talking about angular separation or distance between two galaxies, now I am asking about the distance from us to one galaxy. -- How far away is the furthest galaxy, how fast it moves away?

madus
2012-Nov-02, 08:25 PM
Basic trigonometry says no.

Tell me more.

Grey
2012-Nov-02, 08:27 PM
The third side can not stay fixed if any of the other two sides change.This is incorrect. It's perfectly possible to have a triangle with side lengths of a, b, and c, and then (say) double the length of the first two sides, while keeping the third side fixed, to have a triangle with side lengths of 2a, 2b, and c. You can do this with any triangle, regardless of what values you assign to a, b, and c (try it out if you don't believe me). Of course, the angles don't stay the same in this case. Just to forestall any confusion, that's not was I was originally suggesting, because that's not what happens in cosmological expansion. I think I made it quite clear from the outset that I was suggesting that you envision a triangle where all three sides increase in length uniformly, and in that case, the angles do not change.


And no, if the two sides change uniformly then the third side follows automatically and all the angles would stay the same.Well, again, no. If just two sides change uniformly, whether the angles remain the same depends on whether the third side also expands. Or, looking at it from the other direction, if two sides each increase by the same factor, and the angle between them stays the same, then the third side will also have to increase by the same factor. In the case of cosmological expansion, all three sides increase proportionally at the same time, and so the angles do remain fixed (which you disagreed with initially, insisting that their angular separation should increase), but if we're discussing triangles in general, that's not the only possibility, as I pointed out above.

But I don't think we need to discuss all the general geometrical cases. Originally, you were insisting that two galaxies should move farther apart in the sky due to expansion (i.e., that the angle of separation would change). Am I correct that you now agree that in a uniformly expanding universe, two distant galaxies will not appear to move farther apart in the sky?

Strange
2012-Nov-02, 08:34 PM
Tell me more.

Really?


I'm pretty good with mathematics ...

Come on, this is the sort of thing you would have done in the first year or two of secondary/high school.

mkline55
2012-Nov-02, 08:36 PM
The entire triangle/angle/distance discussion lends no weight to the expansion vs. contraction differences under question. The arguments simply do not favor either model, and the discussion about claiming who said what and who misunderstood what is not helpful.

Grey
2012-Nov-02, 08:39 PM
Before we were talking about angular separation or distance between two galaxies, now I am asking about the distance from us to one galaxy. -- How far away is the furthest galaxy, how fast it moves away?But you'll recall that originally, I assumed you were talking about distance from us to a single galaxy (I assumed that because, as I think we now all agree, angular separation doesn't change as a result of cosmological expansion, so you can't use that method at all). Back here (http://cosmoquest.org/forum/showthread.php/138917-Supporting-evidence-for-the-expanding-universe?p=2075695#post2075695) I pointed out that for a 1% change in distance (which is actually somewhat smaller than our measurement error, but I'm giving us the benefit of the doubt), you'd need to wait about 140 million years. Since the change in distance is always proportional to how far away a galaxy is, it doesn't actually matter if you pick a distant galaxy or a nearby one (as long as it's far enough away that its motion is primarily from cosmological expansion); you'll still have to wait the same length of time for a given percentage change in the distance measurement. As you can see, waiting a few weeks (or even a few centuries) won't be enough to make a measurable difference.

Grey
2012-Nov-02, 08:41 PM
The entire triangle/angle/distance discussion lends no weight to the expansion vs. contraction differences under question. The arguments simply do not favor either model, and the discussion about claiming who said what and who misunderstood what is not helpful.I just want to make sure we're agreed on the basic facts. Do you now agree that the angular separation between two distant galaxies should not be expected to change as a result of cosmological expansion?

cjameshuff
2012-Nov-02, 08:47 PM
It does not contradict as all the angles would remain the same even if only two sides change uniformly. I was simply asking if I understood him correctly.

No, they clearly wouldn't.



Do you agree that even if only two sides change uniformly all the angles would remain the same?

Of course not, as it's obviously wrong. All three sides have to change in the same proportion.



What about interference, diffraction, refraction, scattering and such? What about dark mater, does it have no impact on em-waves?

What sort of "interference" would dim more distant galaxies? How would diffraction, refraction, scattering, etc cause this without having other detectable effects? Where would the scattered light go?

And dark matter is "dark" specifically because it doesn't interact electromagnetically. The closest we get to seeing it is gravitational lensing. It doesn't dim light.



What does it matter how far away they are? The further the better as that means they would be moving away faster, even faster than light, right? -- So what is our resolution, when we measure the distance to the furthest galaxies, what's the error estimate, plus-minus what?

On the order of a few percent at best. Again, that's a few percent of a few billion light years. So yes, the distance matters.

tusenfem
2012-Nov-02, 08:59 PM
I also meant to ask where I can find the list of mainstream journals, so I can avoid using unacceptable references in the future.

Mainstream papers can be found at ADS Abstract Service (http://esoads.eso.org/ads_abstracts.html).

madus
2012-Nov-02, 09:01 PM
This is incorrect. It's perfectly possible to have a triangle with side lengths of a, b, and c, and then (say) double the length of the first two sides, while keeping the third side fixed, to have a triangle with side lengths of 2a, 2b, and c.

Well, again, no. If just two sides change uniformly, whether the angles remain the same depends on whether the third side also expands.


The size of two sides (and angle between them) directly determines the size of the third side and the other two angles in a triangle.




Originally, you were insisting that two galaxies should move farther apart in the sky due to expansion (i.e., that the angle of separation would change). Am I correct that you now agree that in a uniformly expanding universe, two distant galaxies will not appear to move farther apart in the sky?

It was a question, that's opposite of "insisting". Yes, now I understand how this expansion works, so yes I agree all the angular distances would remain the same in such universe.

madus
2012-Nov-02, 09:28 PM
No, they clearly wouldn't.

Of course not, as it's obviously wrong. All three sides have to change in the same proportion.


Take v and V, draw the line on top of them to get two triangles. What angle do you think changed? Do you not see the size of the two sides of V directly determines the size of the top side and all the angles stay the same?




What sort of "interference" would dim more distant galaxies? How would diffraction, refraction, scattering, etc cause this without having other detectable effects? Where would the scattered light go?


Just wondering if that stuff was taken into account. Perhaps some of those interactions could shift spectral lines, or something, and so screw the reference you need to determine the distance.

Strange
2012-Nov-02, 09:34 PM
Take v and V, draw the line on top of them to get two triangles. What angle do you think changed? Do you not see the size of the two sides of V directly determines the size of the top side and all the angles stay the same?

This is, as mkline55 pointed out, a bit of a distraction, but I think it is important to get a common understanding. This may be a language problem but previously you said:

Do you agree that even if only two sides change uniformly all the angles would remain the same?

But now you are saying that all three sides change proportionally (and so, obviously, the angles stay the same).

If only two sides change, then the angles will change.

madus
2012-Nov-02, 09:50 PM
On the order of a few percent at best. Again, that's a few percent of a few billion light years. So yes, the distance matters.

I can not put those numbers into perspective. I expected if some galaxy is moving away from us at 300,000,000m/s, then if not weeks at least in few years it would move away far enough for us to measure some difference. I again don't see how distance matters, unless the error grows proportionally with the distance, is that what you are saying?

madus
2012-Nov-02, 10:10 PM
This is, as mkline55 pointed out, a bit of a distraction, but I think it is important to get a common understanding. This may be a language problem but previously you said:


But now you are saying that all three sides change proportionally (and so, obviously, the angles stay the same).

If only two sides change, then the angles will change.

"Only two" was bad choice of words. But I explained before that it was automatic relation, that you can not change the size of two sides without changing the third side, that's why it did not matter if I was talking about only two sides or all three. Anyway, I guess we understand each other now so let's drop this already.

tusenfem
2012-Nov-02, 10:13 PM
Okay, stop the pointless triangle discussion!

Cougar
2012-Nov-02, 10:30 PM
I can not put those numbers into perspective. I expected if some galaxy is moving away from us at 300,000,000m/s, then if not weeks at least in few years it would move away far enough for us to measure some difference. I again don't see how distance matters, unless the error grows proportionally with the distance, is that what you are saying?

This is real simple math. Why don't you give it a go?

madus
2012-Nov-02, 10:47 PM
This is real simple math. Why don't you give it a go?

Ok. But the number I really want to know I can not calculate - the error estimate and how it depends on distance.

Cougar
2012-Nov-02, 10:58 PM
My original question was simply asking why one position was chosen over the other.

The CMB has been extensively studied. In the cosmological expansion view, the radiation from the CMB we are now detecting left the surface of last scattering when the region of space we now inhabit was only ~42 million lightyears from it! So we're seeing the size of the density variations from that much earlier time. But that radiation has taken over 13 billion years to finally reach us since it has been "swimming upstream," so to speak, through an expanding Universe. The CMB power spectrum shows, from observing the CMB, that the largest variations in the CMB fluctuations is about 1o of arc. This is just what is expected if the surface of last scattering occurred about 380,000 years after the beginning of the expansion (since gravity only had that amount of time to affect anything in its surroundings).

Are you (or Bob) saying that these remarkable findings are just as perfectly and easily explained in a Universe that is not expanding, but contracting? If so, then please do so!

Cougar
2012-Nov-02, 11:04 PM
Ok. But the number I really want to know I can not calculate - the error estimate and how it depends on distance.

The relevant number is how much further the object is away after, say, a year, and compare that to the total billions of lightyears away that the object was to begin with. Even receding at the speed of light, it's only going to get 1 lightyear farther away, isn't it? A change of 1 divided by several billion is probably about 6 orders of magnitude smaller than whatever the error bars are!

madus
2012-Nov-03, 05:58 AM
The relevant number is how much further the object is away after, say, a year, and compare that to the total billions of lightyears away that the object was to begin with. Even receding at the speed of light, it's only going to get 1 lightyear farther away, isn't it? A change of 1 divided by several billion is probably about 6 orders of magnitude smaller than whatever the error bars are!

I don't understand why do you divide it with billions. So anyway, if the error is at least plus-minus several hundreds of light years, how can you say whether a galaxy is moving away at 0.3c or 0.7c, or 10c? - As I see it there is some resolution built in the scale of light intensity we measure and I don't see why or how would that resolution depend on the distance.

Jeff Root
2012-Nov-03, 07:31 AM
The fundamentals of measurement and measurement error
are taught at various grade levels in both math and general
science classes in elementary, middle, and high school, as
well as high school physics. I recommend that you locate a
textbook for any of those which includes extensive coverage
of measurement, and work through the problems. You will
find there what you need to know in order to understand how
distances and motions of distant galaxies are determined,
and all the rest of science along with. It can be fabulously
useful information.

There is no royal road to geometry.

-- Jeff, in Minneapolis

Shaula
2012-Nov-03, 07:43 AM
I don't understand why do you divide it with billions.
Cougar was making precisely the point I made when I did the back-of-envelop calculation for you. The actual distance receded, compared to the distance of the galaxy is tiny. So looking for it using observational methods will not work.


So anyway, if the error is at least plus-minus several hundreds of light years, how can you say whether a galaxy is moving away at 0.3c or 0.7c, or 10c?
We use spectroscopic methods to determine the recessional speeds. We make our best estimates of galactic distance using things like luminosity estimates. We do this over large number of galaxies and find that there is a trend. There is also noise but we are never looking at just one source. We use statistics which drives down the uncertainty problems.

madus
2012-Nov-03, 08:05 AM
Cougar was making precisely the point I made when I did the back-of-envelop calculation for you. The actual distance receded, compared to the distance of the galaxy is tiny. So looking for it using observational methods will not work.


We use spectroscopic methods to determine the recessional speeds. We make our best estimates of galactic distance using things like luminosity estimates. We do this over large number of galaxies and find that there is a trend. There is also noise but we are never looking at just one source. We use statistics which drives down the uncertainty problems.

Can you give me some actual numbers?

Take whatever galaxy:
a.) distance=? : error estimate=?
b.) speed=? : error estimate=?

Shaula
2012-Nov-03, 08:35 AM
http://spiff.rit.edu/classes/phys240/lectures/distant/distant.html has an overview of measurement methods. The one that works to the greatest distance is only 10-15% accurate. There is also a table with approximate accuracies in the link (right at the bottom). There are some links to technical papers on this.

As for recessional speeds - the errors are pretty small. They are also totally instrument dependent. So there is no one simple answer to your question. There are loads of surveys, each with an accuracy dependent on the waveband they cover and the resdhift of the target. Try this paper (http://supernova.lbl.gov/~evlinder/redsys.pdf) for a point sample at z<2 (error is of the order of half a percent). Here (http://heasarc.gsfc.nasa.gov/docs/swift/about_swift/redshift.html)is a piece of SWIFT reporting that shows an error of under 5%.

To be honest that is about as good as you are going to get unless you invest some time and google-fu on this.

madus
2012-Nov-03, 08:53 AM
The fundamentals of measurement and measurement error
are taught at various grade levels in both math and general
science classes in elementary, middle, and high school, as
well as high school physics. I recommend that you locate a
textbook for any of those which includes extensive coverage
of measurement, and work through the problems. You will
find there what you need to know in order to understand how
distances and motions of distant galaxies are determined,
and all the rest of science along with.

You could answer any question like that. Just put it in your signature and you can reply with empty messages then. -- Ok, so now when I have done what you recommended, I'd like to know few specific numbers related specifically to astronomical measurements and error estimates of distant galaxies. Would you be the right person to ask about it?

madus
2012-Nov-03, 08:55 AM
http://spiff.rit.edu/classes/phys240/lectures/distant/distant.html has an overview of measurement methods. The one that works to the greatest distance is only 10-15% accurate. There is also a table with approximate accuracies in the link (right at the bottom). There are some links to technical papers on this.

As for recessional speeds - the errors are pretty small. They are also totally instrument dependent. So there is no one simple answer to your question. There are loads of surveys, each with an accuracy dependent on the waveband they cover and the resdhift of the target. Try this paper (http://supernova.lbl.gov/~evlinder/redsys.pdf) for a point sample at z<2 (error is of the order of half a percent). Here (http://heasarc.gsfc.nasa.gov/docs/swift/about_swift/redshift.html)is a piece of SWIFT reporting that shows an error of under 5%.

To be honest that is about as good as you are going to get unless you invest some time and google-fu on this.

10% - 15%, that's the stuff what I was asking for. Thank you.



method works out to accuracy comments
================================================== =====================
Globular cluster 50 Mpc? 25% ? not entirely consistent
luminosity function with other methods

Type Ia supernovae > 3000 Mpc 8-10% must correct for the
decline rate effect

Brightest Cluster > 3000 Mpc 20-30% must select carefully
Galaxy

Surface Brightness 60 Mpc 5-8% (from ground)
Fluctuations 120 Mpc (from space)

Rotation vs. 1000 Mpc 20% relatively easy to do
Luminosity

Type II supernovae 200 Mpc 15-40% requires spectra of high
quality

gravitational lenses > 5000 Mpc > 25% ? works at huge distances,
but models of lens masses
very uncertain

Bob Angstrom
2012-Nov-03, 09:48 AM
Missing the point entirely. The point is that gravity is a dynamic effect that happens to spacetime so there is no reason things cannot move under the effects of gravity while still undergoing the effect of metric expansion.Everything is under the effect of metric expansion and motion remains possible. That is stating the obvious so I hope that isn't your point. I am guessing your point is that space within a galaxy can expand beyond the galaxy.

Really isn't. No idea where you got this from. Any deviation in the motion of galaxies from the flow of the metric of expansion would require overcoming the resistance known as inertia and this is the rational behind dark energy. This is just a large scale example of inertia and the effect is no different from small scale inertia.
What theoretical underpinning supports this idea? Or does it just sound nice? What is a fog of chaos? How do fogs of chaos give birth to enormous universes ready to contract? What about entropy?This was in response to a perfectly sensible “What if?” question that called for a bit of pure speculation. You can take it or leave it.
Yes there are. Any system is which the thermal fluctuations are sufficient to overcome the gravitational forces, any system in which electric charge or strong forces overcomes gravity is not bound. You seem to be making a ridiculous definition of gravitationally bound here to try to win a point. Just because something may feel an immeasurably small force due to gravity (which might be cancelled by the gravity from somewhere else - another unbound system) does not mean it is bound.I have long been familiar with the concept of “unbound matter” but it always impressed me as a naive way of explaining how space can expand while the galaxies remain unchanged. I have had a chance to do some reading about the topic and I was surprised to find that unbound matter has become a widely accepted term just as you described it. I recognize that there is such a concept and wont try to change the notion but unbound matter doesn't fly from a neo-Machian perspective.

Shaula
2012-Nov-03, 09:52 AM
Any deviation in the motion of galaxies from the flow of the metric of expansion would require overcoming the resistance known as inertia and this is the rational behind dark energy. This is just a large scale example of inertia and the effect is no different from small scale inertia.
You are treating metric expansion like a force. It is not. I am sorry but that seems to be the root of your misunderstanding here. Metric expansion is not a force, you do not have to fight it.

Bob Angstrom
2012-Nov-03, 06:59 PM
You are treating metric expansion like a force. It is not. I am sorry but that seems to be the root of your misunderstanding here. Metric expansion is not a force, you do not have to fight it.I'll explain again. You said,”Gravity is not a static property of spacetime - it is associated with a body and does not just passively expand with metric expansion.” and I said “ Resistance to the metric of expansion is usually called inertia.” The inertia (my word) of ponderous bodies to "not passively expand with metric expansion" (your words) is what needs to be overcome. Dark energy has been proposed as a presently unknown force that does the work. I said nothing about metric expansion as a force.

Bob Angstrom
2012-Nov-03, 07:19 PM
This is extraordinarily misleading. First of all, these early estimates of the total effect of starlight has nothing to do with a microwave background. Last time I looked, stars were not emitting all their radiation in the microwave region of the spectrum. Second of all, these early estimates considered the Milky Way galaxy to be the entire Universe. Do you think the fact that the estimators overlooked over a hundred billion other galaxies in the Universe might have led to a conclusion that was slightly off? If you or mkline are seriously questioning the current understanding of the Cosmic Microwave Background Radiation, then I would have to conclude that you are not only very, very ill-informed, but apparently purposely so.The early astronomers were not looking for microwave radiation coming directly from the stars. How could they? This is a difficulty that a great many people have with understanding Eddington's “thermometer in space” We all remember the miners in Chile who were trapped for so long beneath the ground. They were insulated from all major sources of heat by more than a thousand feet of rock in every direction but the temperature in the mine was not zero K. It was uncomfortably warm because they were heated by re-radiated thermal emissions from several sources. They were heated from below by the friction of tidal stresses and by natural radiation and they were heated from above by radiant emission from the sun and this was likely their major source of heat. The sun is a star so they were heated by re-radiated starlight as incredible as that may sound. Objects heated by the sun (starlight) should not be expected to re-radiate that energy with the same spectrum as the sun and observing the thermal emissions from something non-luminous like the walls of a mine does not identify the initial source or sources of energy.

Eddington speculated that all non-luminous matter in space should absorb EM emissions just as it does on Earth so interstellar matter should have a non-zero temperature somewhere above absolute and this temperature was Eddington's “thermometer in space.” The astronomers were looking for a background radiation from non-luminous matter (dust gases etc.) that was echoing about being absorbed and re-emitted many times over giving space an observable ambient temperature. They were not looking for stars radiating at 3 K. They found temperatures inside the Milky Way to be higher than the extra-galactic temperature of 3 K and this is exactly what we should expect.

Shaula
2012-Nov-03, 07:27 PM
Objects heated by the sun (starlight) should not be expected to re-radiate that energy with the same spectrum as the sun and observing the thermal emissions from something non-luminous like the walls of a mine does not identify the initial source or sources of energy.

However neither should cold dust grains be expected to re-radiate as a perfect black body.

Bob Angstrom
2012-Nov-04, 04:54 PM
However neither should cold dust grains be expected to re-radiate as a perfect black body.All thermal spectra merge towards the perfect black body energy spectrum at extremely low temperatures so it is a dubious claim that Eddington's model and the CMBR spectrum would look any different. Both stellar fusion and the theoretical CMBR are thermal sources and, like all forms of EM radiation, they can be absorbed and re-emitted by cold matter. I find it hard to imagine that a primal energy source like the CMBR could exist for billions of years without at some point being absorbed and re-emitted by some form of cold matter making the the source of the spectrum we observe identical in either case.*

Shaula
2012-Nov-04, 05:08 PM
All thermal spectra merge towards the perfect black body energy spectrum at extremely low temperatures so it is a dubious claim that Eddington's model and the CMBR spectrum would look any different. Both stellar fusion and the theoretical CMBR are thermal sources and, like all forms of EM radiation, they can be absorbed and re-emitted by cold matter. I find it hard to imagine that a primal energy source like the CMBR could exist for billions of years without at some point being absorbed and re-emitted by some form of cold matter making the the source of the spectrum we observe identical in either case.*
Even if there were cold matter absorbers capable of doing this (there are not) - the radiation would have to interact with matter relatively locally. Otherwise the redshift would distort the spectrum away from a pure blackbody. Your idea calls for a huge matter density locally, otherwise we have to drop redshift and expansion/contraction. This matter would show up observationally.

The universe is really quite empty, you know. It is perfectly possible for the CMBR to have interacted with relatively little matter. No matter how incredulous of this you are.

It is worth stating: I have no objections in a GR treatment of the universe being expressed as contraction. Trying to add in QM makes this picture more complex than it needs to be, however, which is why I prefer expansion. I have a big issue with this alternative cosmology you seem to be tacking on to this to try to make contraction appear more appealing. The evidence is against it. The CMBR is best explained by the surface of last scattering. There are not quadrillions of tonnes of perfectly black dust grains uniformly distributed around us.

Cougar
2012-Nov-07, 02:00 PM
This is a difficulty that a great many people have with understanding Eddington's “thermometer in space” We all remember the miners in Chile....

Way to dodge the issue, Bob. And condescendingly! Such misguided talent!